MANUFACTURE OF ROLL TAR PAPER.

Roofing paper was first used in Scandinavia early as the last century,

the invention being accredited to Faxa, an official of the Swedish

Admiralty. The first tar and gravel roofs in Sweden were very

defective. The impregnation of the paper with a water-proofing liquid

had not been thought of, and the roofs were constructed by laying over

the rafters a boarding, upon which the unsaturated paper, the sides of

which lapped over the other, was fastened with short tacks. The

surface of the paper was next coated with heated pine tar to make it

waterproof. The thin layer of tar was soon destroyed by the weather,

so that the paper, swelled by the absorption of rain water, lost its

cohesiveness and was soon destroyed by the elements. This imperfect

method of roof covering found no great favor and was but seldom

employed.

In Germany the architect Gilly was first to become interested in tar

paper roofing, and recommended it in his architecture for the country.

Nevertheless the new style of roof covering was but little employed,

and was finally abandoned during the first year of the 19th century.

It was revived again in 1840, when people began to take a renewed

interest in tar paper roofs, the method of manufacturing an

impermeable paper being already so far perfected that the squares of

paper were dipped in tar until thoroughly saturated. The roof

constructed of these waterproof paper sheets proved itself to be a

durable covering, being unimpenetrable to atmospheric precipitations,

and soon several factories commenced manufacturing the paper. The

product was improved continually and its method of manufacture

perfected. The good qualities of tar paper roofs being recognized by

the public, they were gradually adopted. The costly pine tar was soon

replaced by the cheaper coal tar. Square sheets of paper were made at

first; they were dipped sufficiently long in ordinary heated coal tar,

until perfectly saturated. The excess of tar was then permitted to

drip off, and the sheets were dried in the air. The improvement of

passing them through rollers to get rid of the surplus tar was

reserved for a future time, when an enterprising manufacturer

commenced to make endless tar paper in place of sheets. Special

apparatus were constructed to impregnate these rolls with tar; they

were imperfect at first, but gradually improved to a high degree. Much

progress was also made in the construction of the roofs, and several

methods of covering were devised. The defects caused by the old method

of nailing the tar paper direct upon the roof boarding were corrected;

the consequence of this method was that the paper was apt to tear,

caused by the unequal expansion of the roofing boards and paper, and

this soon led to the idea of making the latter independent of the

former by nailing the sides of the paper upon strips running parallel

with the gable. The use of endless tar paper proved to be an essential

advantage, because the number of seams as well as places where it had

to be nailed to the roof boarding was largely decreased. The

manufacture of tar paper has remained at about the same stage and no

essential improvements have been made up to the present. As partial

improvement may be mentioned the preparation of tar, especially since

the introduction of the tar distillery, and the manufacture of special

roof lacquers, which have been used for coating in place of the coal

tar. As an essential progress in the tar paper roofing may be

mentioned the invention of the double tar paper roof, and the wood

cement roof, which is regarded as an offshoot.

The tar paper industry has, within the last forty years, assumed great

dimensions, and the preferences for this roofing are gaining ground

daily. In view of the small weight of the covering material, the wood

construction of the roof can be much lighter, and the building is

therefore less strained by the weight of the roof than one with the

other kind, so that the outer walls need not be as heavy. Considering

the price, the paper roof is not only cheaper than other fireproof

roofs, but its light weight makes it possible for the whole building

to be constructed lighter and cheaper. The durability of the tar paper

roof is satisfactory, if carefully made of good material; the double

tar paper roof, the gravel double roof, and the wood cement roof are

distinguished by their great durability.

These roofs may be used for all kinds of buildings, and not only are

factories, storehouses, and country buildings covered with it, but

also many dwellings. The most stylish residences and villas are at

present being inclosed with the more durable kinds; the double roof,

the gravel double roof, and the wood cement roof. For factory

buildings, which are constantly shaken by the vibrations of the

machinery, the tar paper roof is preferable to any other.

In order to ascertain to what degree tar paper roofs would resist

fire, experiments were instituted at the instigation of some of the

larger manufacturers of roofing paper, in the presence of experts,

architects, and others, embracing the most severe tests, and it was

fully proved that the tar paper roof is as fireproof as any other.

These experiments were made in two different ways; first, the

readiness of ignition of the tar paper roof by a spark or flame from

the outside was considered, and, second, it was tested in how far it

would resist a fire in the interior of the building. In the former

case, it was ascertained that a bright, intense fire could be kept

burning upon the roof for some time, without igniting the woodwork of

the roof, but heat from above caused some of the more volatile

constituents of the tar to be expelled, whereby small flames appeared

upon the surface within the limits of the fire; the roofing paper was

not completely destroyed. There always remained a cohesive substance,

although it was charred and friable, which by reason of its bad

conductivity of heat protected the roof boarding to such an extent

that it was "browned" only by the developed tar vapors. A fire was

next started within a building covered with a tar paper roof; the

flame touched the roof boarding, which partly commenced to char and

smoulder, but the bright burning of the wood was prevented by the

air-tight condition of the roof; the fire gases could not escape from

the building. The smoke collecting under the roof prevented the

entrance of fresh air, in consequence of which the want of oxygen

smothered the fire. The roofing paper remained unchanged. By making

openings in the sides of the building so that the fire gases could

escape, the wood part of the roof was consumed, but the roofing paper

itself was only charred and did not burn. After removing the fire in

contact with the paper, this ceased burning at once and evinced no

disposition whatever to spread. In large conflagrations, also, the tar

paper roofs behaved in identically a similar manner. Many instances

have occurred where the tar paper roof prevented the fire from

spreading inside the building, and developing with sufficient

intensity to work injury.

As it is of interest to the roofer to know the manner of making the

material he uses, we give in the following a short description of the

manufacture of roofing paper. At first, when square sheets were used

exclusively, the raw paper consisted of ordinary dipped or formed

sheets. The materials used in its manufacture were common woolen rags

and other material. In order to prepare the pulp from the rags it is

necessary to cut them so small that the fabric is entirely dissolved

and converted into short fibers. The rags are for this purpose first

cut into pieces, which are again reduced by special machines. The rags

are cut in a rag cutting machine, which was formerly constructed

similar to a feed cutter; later on, more complicated machines of

various constructions were employed. It is not our task to describe

the various kinds, but we remain content with the general remark that

they are all based on the principles of causing revolving knives to

operate upon the rags. The careful cleansing of the cut rags,

necessary for the manufacture of paper, is not required for roofing

paper. It is sufficient to rinse away the sand and other solid

extraneous matter. The further reduction of the cut rags was formerly

performed in a stamp mill, which is no longer employed, the pulp mill

or rag engine being universally used.

The construction of this engine may be described as follows: A box or

trough of wood, iron, or stone is by a partition divided into two

parts which are connected at their ends. At one side upon the bottom

of the box lies an oakwood block, called the back fall. In a hollow of

this back fall is sunk the so-called plate, furnished with a number of

sharp steel cutters or knives, lying alongside of each other. A roller

of solid oakwood, the circumference of which is also furnished with

sharp steel cutters or knives, is fastened upon a shaft and revolves

within the hollow. The journal bearings of the shaft are let into and

fastened in movable wooden carriers. The carriers of the bearings may

be raised and lowered by turning suitable thumbscrews, whereby the

distance between the roller and the back fall is increased or

decreased. The whole is above covered with a dome, the so-called case,

to prevent the throwing out of the mass under the operation of

grinding. The roller is revolved with a velocity of from 100 to 150

revolutions per minute, whereby the rags are sucked in between the

roller and the back fall and cut and torn between the knives. At the

beginning of the operation, the distance between the roller and the

back fall is made as great as possible, the intention being less to

cut the rags than to wash them thoroughly. The dirty water is then

drawn off and replaced by clean, and the space of the grinding

apparatus is lessened gradually, so as to cut the rags between the

knives. The mass is constantly kept in motion and each piece of rag

passes repeatedly between the knives. The case protects the mass from

being thrown out by the centrifugal force. The work of beating the

rags is ended in a few hours, and the ensuing thin paste is drawn off

into the pulp chest, this being a square box lined with lead.

From the pulp chest it passes to the form of the paper machine. This

form consists of an endless fine web of brass wire, which revolves

around rollers. The upper part of this form rests upon a number of

hollow copper rollers, whereby a level place is formed. The form

revolves uniformly around the two end rollers, and has at the same

time a vibratory motion, by which the pulp running upon the form is

spread out uniformly and conducted along, more flowing on as the

latter progresses. The water escapes rapidly through the close wire

web. In order to limit the form on the sides two endless leather

straps revolve around the rollers on each side, which touch with their

lower parts the form on both sides and confine the fluid within a

proper breadth. The thickness of the pulp is regulated at the head of

the form by a brass rule standing at a certain height; its function is

to level the pulp and distribute it at a certain thickness. The

continually moving pulp layer assumes greater consistency the nearer

it approaches to the dandy roll. This is a cylinder covered with brass

wire, and is for the purpose of compressing the paper, after it has

left the form, and free it from a great part of the water, which

escapes into a box. The paper is now freed of a good deal of the

fluid, and assumes a consistency with which it is enabled to leave the

form, which now commences to return underneath the paper, passing on

to an endless felt, which revolves around rollers and delivers it to

two iron rolls. The paper passes through a second pair of iron

rollers, the interiors of which are heated by steam. These rollers

cause the last of the water to be evaporated, so that it can then be

rolled upon reels. A special arrangement shaves the edges to the exact

size required.

The paper is made in different thicknesses and designated by numbers

to the size and weight.

Waste paper, bookbinders' shavings, etc., can be used for making the

paper. As much wool as possible should be employed, because the wool

fiber has a greater resistance than vegetable fiber to the effects of

the temperature. By wool fiber is understood the horny substance

resembling hair, with the difference that the former has no marrowy

tissue. The covering pellicle of the wool fiber consists of flat,

mostly elongated leaves, with more or less corners, lying over each

other like scales, which makes the surface of the fiber rough; this

condition, together with the inclination of curling, renders it

capable of felting readily. Pure wool consists of a horny substance,

containing both nitrogen and sulphur, and dissolves in a potash

solution. In a clean condition, the wool contains from 0.3 to 0.5 per

cent. of ash. It is very hygroscopical, and under ordinary

circumstances it contains from 13 to 16 per cent. humidity, in dry air

from 7 to 11 per cent., which can be entirely expelled at a

temperature of from 226 to 230 degrees Fahrenheit. Wool when ignited

does not burn with a bright flame, as vegetable fiber does, but

consumes with a feeble smouldering glow, soon extinguishes, spreading

a disagreeable pungent vapor, as of burning horn. By placing a test

tube with a solution of five parts caustic potash in 100 parts water,

a mixture of vegetable fibers and wool fibers, the latter dissolve if

the fluid is brought to boiling above an alcohol flame, while the

cotton and linen fibers remain intact.

The solubility of the woolen fibers in potash lye is a ready means of

ascertaining the percentage of wool fiber in the paper. An exhaustive

analysis of the latter can be performed in the following manner: A

known quantity of the paper is slowly dried in a drying apparatus at

temperature of 230° Fahrenheit, until a sample weighed on a scale

remains constant. The loss of weight indicates the degree of humidity.

To determine the ash percentage, the sample is placed in a platinum

crucible, and held over a lamp until all the organic matter is burned

out and the ash has assumed a light color. The cold ash is then

moistened with a carbonate of ammonia solution, and the crucible again

exposed until it is dark red; the weight of the ash is then taken. To

determine the percentage of wool, a sample of the paper is dried at

230° Fahrenheit and weighed, boiled in a porcelain dish in potash lye

12° B. strong, and frequently stirred with a glass rod. The wool fiber

soon dissolves in the potash lye, while the vegetable fiber remains

unaltered. The pulpy mass resulting is placed upon a filter, dried at

212° Fahrenheit, and after the potash lye has dripped off, the

residue, consisting of vegetable fiber and earthy ash ingredients, is

washed until the water ceases to dissolve anything. The residue dried

at 212° Fahrenheit is weighed with a filter, after which that of the

latter is deducted. The loss of weight experienced is essentially

equal to the loss of the wool fiber. If the filtrate is saturated with

hydrochloric acid, the dissolved wool fiber separates again, and after

having been collected upon a weighed filter, it may be weighed and the

quantity ascertained.

The weight of the mineral substances in the raw paper is ascertained

by analyzing the ash in a manner similar to that above described. The

several constituents of the ash and the mineral added to the raw paper

are ascertained as follows: Sufficient of the paper is calcined in the

manner described; a known quantity of the ash is weighed and thrown

into a small porcelain dish containing a little distilled water and an

excess of chemically pure hydrochloric acid. In this solution are

dissolved the carbonates, carbonate of lime, carbonate of magnesia, a

little of sulphate of alumina, as well as metallic oxides, while

silicate of magnesia, silicic acid, sulphate of lime (gypsum) remain

undissolved. The substance is heated until the water and excess of

free hydrochloric acid have been driven off; it is then moistened with

a little hydrochloric acid, diluted with distilled water and heated.

The undissolved residue is by filtering separated from the dissolved,

the filter washed with distilled water, and the wash water added to

the filtrate. The undissolved residue is dried, and after the filter

has also been burned in due manner and the ash added, the weight is

ascertained. It consists of clay, sand, silicic acid and gypsum.

The filtrate is then poured into a cylinder capable of holding 100

cubic centimeters, and furnished with a scale; sufficient distilled

water is then added until the well-shaken fluid measures precisely 100

cubic centimeters. By means of this measuring instrument, the filtrate

is then divided into two equal portions. One of these parts is in a

beaker glass over-saturated with chemically pure chloride of ammonia,

whereby any iron of oxide present and a little dissolved alumina fall

down as deposit. The precipitate is separated by filtering, washed,

dried at 212° Fahrenheit and weighed. To the filtrate is then added a

solution of oxalate of ammonia until a white precipitate of oxalate of

lime is formed. This precipitate is separated by filtering, washed,

dried and when separated from the filter, is collected upon dark

satinized paper; the filter itself is burned and the ash added to the

oxalate of lime. This oxalate of lime is then heated to a dark red

heat in a platinum crucible with lid until the oxalate of lime is

converted into carbonate of lime. By the addition of a few drops of

carbonate of ammonia solution and another slight heating of the

crucible, also the caustic lime produced in the filter ash by heating,

is reconverted into carbonate of lime, and after cooling in the

exsiccator, the whole contents of the crucible is weighed as

carbonate of lime, after deducting the known quantity of filter ash.

Any magnesia present in the filtrate of the oxalate of lime is by the

addition of a solution of phosphate of soda separated as phosphate of

ammonia and magnesia, after having stood twenty-four hours. The

precipitate is filtered off, washed with water to which a little

chloride of ammonia is added, dried, and after calcining the fiber and

adding the filter ash, glow heated in the crucible. The glowed

substance is weighed after cooling, and is pyrophosphate of magnesia,

from which the magnesia or carbonate of magnesia is calculated

stoichiometrically. All the ascertained sums must be multiplied by 2,

if they are to correspond to the analyzed and weighed quantity of ash.

The second half of the filtrate is used for determining the small

quantity of sulphate of lime still contained in the hydrochlorate

solution. By adding chloride of barium solution the sulphuric acid is

bound to the barytes and sulphate of baryta separates as white

precipitate. This is separated by filtering, washed, dried and weighed

in the customary manner. From the weight of the sulphate of baryta is

then computed the weight of sulphate of lime, which has passed over

into solution. The ascertained sum is also to be multiplied with 2.

The manufacture of roll tar paper from the roll paper was at first

found to be difficult, as it was impossible to submerge a surface

larger than from ten to fifteen square yards, rolled up, in the tar,

because more would have required too large a pan. Besides this, the

paper tears easily, when it is in the hot tar. All kinds of

experiments were tried, in order to impregnate the surface of the

paper without employing too large a pan.

The following method was tried at first: The roll paper was cut into

lengths of ten yards, which were rolled up loosely, so that a certain

space was left between the different coils. These loose rolls, of

course, occupied much space and could be put into the tar only in a

standing position, because in a horizontal one the several coils would

have pressed together again. The loose roll was therefore slipped over

a vertical iron rod fastened into a circular perforated wooden foot.

The upper end of this iron rod ended in a ring, in which the hook of a

chain or rope could be fastened. With the aid of a windlass the roll

was raised or lowered. When placed in the pan with boiling tar, it was

left there until thoroughly saturated. It was then taken out, placed

upon a table, and the excess of tar allowed to drip off into a vessel

underneath. After partially drying, the roll was spread out in open

air, occasionally turned, until sufficiently dried, when it was rolled

up again.

In order to neutralize the smeary, sticky condition of the surface and

avoid the disagreeable drying in open air, the experiment of strewing

sand on the sticky places was tried next. The weight of the paper was

largely increased by the sand, and appeared considerably thicker. For

this reason the method of sanding the paper was at once universally

adopted. To dispense with the process of permitting the surplus tar to

drip off, means were devised by which it was taken off by scrapers, or

by pressing through rollers. The scrapers, two sharp edged rods

fastened across the pan, were then so placed that the paper was drawn

through them. The excess of tar adhering to its surface was thereby

scraped off and ran back into the pan.

This work, however, was performed better and to more satisfaction by a

pair of rollers fastened to the pan. These performed a double duty;

thoroughly removed the tar from the surface and by reason of their

pressure they caused a more perfect incorporation of the tar with the

fibers of the paper. Finally, different factories employed different

methods of manufacture, one of which was to cut the rolls into

definite lengths of about ten yards; these were then rerolled very

loosely and immersed in the hot tar until sufficiently saturated. The

paper was then passed through the roller, much pressure exerted, and

then loosely rolled up again. Being tarred once, it was then laid into

a second pan with hot tar, reeled out after a time, strewn with sand,

and rolled up again. Another method was to cut clothes lines into

lengths of about fifteen yards, and at a distance of two inches have

knots tied in them. The paper was cut in lengths of ten or fifteen

yards, three pieces of the knotted clothes line were then rolled

between the loose coils of paper, which was then submerged in the tar,

which on account of the knots could penetrate the paper. The paper was

next sanded by permitting its lower surface to pass over dry sand in a

box standing on the floor. A workman rolled off the paper, and with

his hand he strews sand on the upper surface. The rolling taking place

on the edge of a table, by means of a crank, the excess of sand

dropped off.

It is said by this method two workmen, one of which tends to the

rolling and sanding, the other turning the crank, could turn out

eighty rolls per day. This method is still in use. It is useless to

describe the many antiquated methods in vogue in smaller factories,

and it can truthfully be said that nearly all of them are out of date.

It appears to be the fact of almost all inventions that when reduced

to practical use, the arrangements, apparatus, and working methods

employed are generally of the most complicated nature, and time and

experience only will simplify them. This has been also the case with

the methods in the roofing paper industry, which are at present

gradually being reduced to a practical basis. The method gradually

adopted has been described in the preceding. The pan is of a certain

length, whereby it becomes possible to saturate the paper by slowly

drawing it through the heated tar. This is the chief feature. The work

is much simplified thereby and the workmen need not dip their hands

into the tar or soil them with it. The work of impregnating has become

much cleaner and easier, while at the same time the tar can be heated

to a much higher temperature. The pan is generally filled with

distilled coal tar, and the heating is regulated in such a manner that

the temperature of the impregnating mass is raised far beyond 212°

Fahrenheit. This accelerates the penetration, which takes place more

quickly as the degree of heat is raised, which may be almost up to the

boiling point of the tar, as at this degree the paper is not destroyed

by the heat. In order to prevent the evaporation of the volatile

ingredients of the tar, the pan is covered with a sheet iron cover,

with a slot at the place where the paper enters into the impregnating

mass and another at the place where it issues. The tar is always kept

at the same level, by occasional additions.

The roll of paper is mounted upon a shaft at the back end of the pan,

and by suitable arrangement of guide rollers it unwinds slowly, passes

into the tar in which it is kept submerged. The guide rollers can be

raised so that when a new roller is set up they can be raised out of

the tar. The end of the paper is then slipped underneath them above

the surface of the tar, when having passed through the squeezing

rollers, it is fastened to the beaming roller, and the guide rollers

are submerged again. A workman slowly turns the crank of the beaming

roller.

This motion draws the paper slowly through the fluid, the roll at the

back end unwinding. The speed with which the squeezing rollers are

turned is regulated in such a manner that the paper remains

sufficiently long underneath the fluid to be thoroughly impregnated

with it. The workmen quickly learn by experience how fast to turn the

crank. The hotter the tar, the more rapid the saturation; the high

degree of heat expels the air and evaporates the hygroscopic fluid in

the pores of the paper. The strong heating of the tar causes another

advantage connected with this method. The surface of the paper as it

issues from the squeezing rollers is still very hot, and a part of the

volatile oils evaporate very quickly at this high temperature. The

surface is thereby at once dried to a certain degree and at the same

time receives a handsome luster, as if it had been coated with a black

lacquer. The paper is sanded in a very simple manner without the use

of mechanical apparatus; as it is being wrapped into a coil, it passes

with its lower surface over a layer of sand, while the workman who

tends to rolling up strews the inside with sand. The lower surface is

coated very equally. Care only being necessary that the sand lies

smooth and even at all times. When the workman has rolled up ten or

fifteen yards, he cuts it across with a knife and straightedge, so

that the paper is cut at right angles with its sides.

There are three different sorts of roofing paper, according to the

impregnating fluid used in its manufacture. The ordinary tar paper is

that saturated with clear cold tar. This contains the greatest amount

of fluid ingredients and is very raggy in a fresh condition. It is

easy to see that the volatile hydrocarbons evaporate in a short time,

and when expelled, the paper becomes stiffer and apparently drier.

This drying, or the volatilization of the hydrocarbons, causes pores

between the fibers of the paper. These pores are highly injurious to

it, as they facilitate a process of decomposition which will ruin it

in a short time.

Roofing paper can be called good only when it is essentially made from

woolen rags, and contains either very few or no earthy additions. It

is beyond doubt that the durability of a roofing paper increases with

the quality of wool fiber it contains--vegetable fibers and earthy

additions cause a direct injury. Reprehensible altogether is any

combination with lime, either in form of a carbonate or sulphate,

because the lime enters into chemical combination with the

decomposition products of the tar.

The general nature of gravel is too well known to require description.

The grains of quartz sand are either sharp cornered or else rounded

pieces of stone of quartz, occasionally mixed with grains of other

amorphous pieces of silica--such as horn stone, silicious slate,

carnelian, etc.; again, with lustrous pieces of mica, or red and white

pieces of feldspar. The gravel used for a tar paper roof must be of a

special nature and be prepared for the purpose. The size of its grains

must not exceed a certain standard--say, the size of a pea. When found

in the gravel bank, it is frequently mixed with clay, etc., and it

cannot be used in this condition for a roof, but must be washed. The

utensils necessary for this purpose are of so simple and suggestive a

nature that they need not be described. Slag is being successfully

used in place of the gravel. It is easily reduced to suitable size, by

letting the red hot mass, as it runs from the furnace, run into a

vessel with water. The sudden chilling of the slag causes it to burst

into fragments of a sharp cornered structure. It is next passed

through a sieve, and the suitably sized gravel makes an excellent

material, as it gives a clean appearance to the roof.

The thinking mind can easily go one step further and imagine that,

since the tar contains a number of volatile hydrocarbons, it might be

made more adaptable for impregnation by paper by distilling it, as by

this process the fluid would lose its tendency to evaporate and the

percentage of resinous substances increase. Singular to say, there was

a prejudice against the employment of distilled tar, entertained by

builders and people who had no knowledge of chemistry. Increasing

intelligence and altered business circumstances, however, brought

about the almost universal employment of distilled tar, and every

large factory uses it at present. The roofing paper prepared with

distilled tar is perhaps most suitably called asphaltum paper, as this

has been used in its manufacture. It possesses properties superior to

the ordinary tar paper, one of which is that immediately after its

manufacture, as soon as cold, it is dry and ready for shipment; nor

does it require to be kept in store for a length of time, and it has

also a good, firm body, being as flexible and tough as leather. It is

very durable upon the roof, and remains flexible for a long time. It

is true that asphaltum papers will always in a fresh state contain a

small percentage of volatile ingredients, which after a while make it

hard and friable upon the roof; but, by reason of its greater

percentage of resinous components, it will always preserve a superior

degree of durability and become far less porous. One hundred parts by

weight absorb 140 or 150 parts by weight of coal tar. A factory which

distilled a good standard tar for roofing paper recovered, besides

benzole and naphtha, also about ten per cent. of creosote oil, used

for one hundred parts raw paper, 176.4 partially distilled tar.

Experiments on a larger as well as a smaller scale reduced this

quantity to an average of 141.5 parts for one hundred parts raw paper.

The weight of sanded paper is very variable, as it depends altogether

upon the size of the sand grains. It may be stated generally that the

weight of the sand is as large as that of the tarred paper.

The kinds of roofing paper saturated with other additions besides coal

tar form a separate class, in order to neutralize the defects inherent

in coal tar. These additions were originally for the purpose of

thickening the paper and making it stiffer and drier. The most

ordinary and cheapest thickener was the coal pitch. Although the

resinous substances are increased thereby, still the light tar oils

remain to evaporate, and the paper prepared with such a substance

readily becomes hard and brittle. A better addition is the natural

asphaltum, because it resists better the destroying influence of the

decomposition process, and also, to a certain degree, protects the

coal tar in which it is dissolved. The addition of natural asphaltum

doubtless caused the name of "asphaltum roofing paper." Resin,

sulphur, wood tar and other substances were also used as additions;

each manufacturer kept his method secret, however, and simply pointed

out by high sounding title in what manner his paper was composed. In

most cases, however, this appellation was applied to the ordinary tar

paper; the impregnating substance was mixed only with coal pitch, or

else a roofing paper saturated with distilled tar. The costly

additions, by the use of which a high grade of roofing paper can

doubtless be produced, largely increased its price, and on account of

the constant fall of prices of the article, its use became rather one

of those things "more honored in the breach than in the observance,"

and was dispensed with whenever practicable. The crude paper is the

foundation of the roofing paper. The qualities of a good,

unadulterated paper have already been stated. At times, the crude

paper contains too many earthy ingredients which impair the cohesion

of the felted fibrous substance, and which especially the carbonate of

lime is very injurious, as it readily effects the decomposition of the

coal tar. The percentage of wool, upon which the durability of the

paper depends very largely, is very small in some of the paper found

in the market. In place of woolen rags, cheap substitutes have been

used, such as waste, which contains vegetable fibers. Since this

cannot resist the decomposition process for any length of time, it is

evident that the roofing paper which contains a noticeable quantity of

vegetable fibers cannot be very durable. To judge from the endeavors

made to improve the coal tar, it may be concluded that this material

does not fully comply with its function of making the roofing paper

perfectly and durably waterproof. The coal tar, be it either crude or

distilled, is not a perfect impregnating material, and the roofing

paper, saturated with it, possesses several defects. Let us in the

following try to ascertain their shortcomings, and then express our

idea in what manner the roofing paper may be improved. It was

previously mentioned that every tar roofing paper will, after a

greater or smaller lapse of time, assume a dry, porous, friable

condition, caused by the volatilization of a part of the constituents

of the tar. This alteration is materially assisted by the oxygen of

the air, which causes the latter to become resinous and exerts a

chemical influence upon them. By the volatilization of the lighter tar

oils, pores are generated between the fibers of the roofing paper,

into which the air and humidity penetrate. In consequence of the

greatly enlarged surface, not only the solid ingredients of the tar,

which still remain unaltered, are exposed to the action of the oxygen,

but also the fibers of the roofing paper are exposed to decomposition.

How destructive the alternating influence of the oxygen and the

atmospheric precipitations are for the roofing paper will be shown by

the following results of tests. It will have been observed that the

rain water running from an old paper roof, especially after dry

weather, has a yellowish, sometimes a brown yellow color. The

supposition that this colored rain water might contain decomposition

products of the roofing paper readily prompted itself, and it has been

collected and analyzed at different seasons of the year. After a

period of several weeks of fair weather during the summer, rain fell,

and the sample of water running from a roof was caught and evaporated;

the residue when dried weighed 1.68 grammes. It was of a brownish

black color, fusible in heat and readily soluble, with a yellow brown

color in water. The dark brown substance readily dissolved in ammonia,

alcohol, dilute acid, hydrochloric acid, sulphuric acid, and

decomposed in nitric acid, but did not dissolve in benzine or fat oil.

After several days' rain during the summer, a quantity of the water

was caught, evaporated, and the residue dried. Its characteristics

were similar to those above mentioned. By an experiment instituted in

water under conditions similar to the first mentioned, the dry brown

substance weighed 71 grammes. It possessed the same characteristics.

In the solution effected with water containing some aqua ammonia of

the brown substance, a white precipitate of oxalate of lime occurred

when an oxalate of ammonia solution was added, but the brown substance

remained in solution. A further precipitation of oxalate of lime was

produced by a solution of oxalic acid, but the brown organic substance

remained in solution. This organic substance being liberated from the

lime was evaporated, and left a dry, resinous, fusible brownish black

substance, which also dissolved readily in water. It will be seen from

these trials that the substance obtained from the rain water running

from a paper roof is a combination of an organic acid with lime, which

readily dissolves in water, and that also the free organic acid

combined with the lime dissolves easily in water.

The question concerning the origin of this organic substance or its

combination with lime can only be answered in one way, viz., that it

must have been washed by the rain water out of the paper. But since

such a solid substance, easily soluble in water, is contained neither

in the fresh roofing paper nor in the coal tar, the only deduction is

that it must have arisen by the decomposition of the tar, in

consequence of the operation of the oxygen. The lime comes from the

coating substance of the roof, for which tar mixed with coal pitch was

used. The latter was fused with carbonate of lime. These analyses

furthermore show that the formation of the organic acid easily soluble

in water depends upon the season; and that a larger quantity of it is

generated in warm, sunny weather than in cold, without sunshine. This

peculiarity of the solid, resinous constituents of the coal tar, to be

by the operation of the atmospheric oxygen altered into such products

that are readily soluble in water, makes the tar very unsuitable as a

saturative substance for a roofing paper. How rapidly a paper roof can

be ruined by the generation of this injurious organic acid will be

seen from the following calculation: Let us suppose that an average

of 132 gallons of rain water falls upon ten square feet roof surface

per year, and that the arithmetical mean 0.932 of the largest (1.680)

and smallest number (0.184) be the quantity of the soluble brown

substance which on an average is dissolved in one quart of rain water;

hence from ten square feet of roof surface are rinsed away with the

rain water per year 466 grammes of the soluble decomposition products

of the tar. The oxidation process will not always occur as intensely

as by a paper roof, ten years old and painted two years ago, which

instigated above described experiment. As long as the roofing paper is

fresh and less porous, especially if the occurring pores are filled

and closed again by repeated coatings, oxidation will take place far

less rapidly. Besides this, the protective coating applied to the roof

surface is exposed most to this oxidation process. Even by assuming

this constantly progressive destructive action of the oxygen on the

roofing paper to be much less than above stated, we can readily

imagine that it must be quite large. If it is desired to produce a

material free of faults, it is first of all indispensable that

unobjectionable raw material be procured. Coal tar was formerly used

almost exclusively for the coating of a roof. It was heated and

applied hot upon the surface. In order to avoid the running off of the

thinly fluid mass, the freshly coated surface was strewn with sand.

The most volatile portion of the tar evaporated soon, whereby the

coating became thicker and finally dried. The bad properties of the

coal tar, pointed out elsewhere, made it very unsuitable even for this

purpose, and experiments were instituted to compound mixtures, by

adding other ingredients to the tar, that should more fully comply

with its function. It may be said in general that the coating masses

for roofs can be divided into two classes: either as lacquers or as

cements. To the former may be classed those of a fairly thinly fluid

consistency, and which contain volatile oils in such quantities that

they will dry quickly. Cements are those of a thickly fluid

consistency, and are rendered thus fluid by heating. It is not

necessary that the coating applied should harden quickly, as it

assumes soon after its application a firmness sufficient to prevent it

from running off the roof. Coal tar is to be classed among lacquers.

If it has been liberated by distillation from the volatile oils, it is

made better suited for the purpose than the ordinary kind. The mass

contains much more asphaltum, and after drying, which takes place

soon, it leaves a far thicker layer upon the roof surface, while the

pores, which had formed in the roofing paper consequent on drying, are

better filled up. Nevertheless, the distilled tar also has retained

the property of drying with time into a hard, vitreous mass, and

ultimately to be destroyed by decomposition.--_The Roofer_.

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