_Classification._--In classifying the different dyestuffs an_The Chemistry of Hat Manufacturing Lectures Delivered Before the Hat Manufacturers' Association

matters it is, of course, necessary to consider first the properties of

those colouring matters generally, and secondly the particular reason

for making such classification. The scientific chemist, for example,

would classify them according to theoretical considerations, as members

of certain typical groups; the representative of medical science or

hygiene would naturally classify them as poisonous and non-poisonous

bodies; whilst the dyer will as naturally seek to arrange them according

to their behaviour when applied to textile fabrics. But this behaviour

on applying to textile fibres, if varied in character according to the

chemical nature of the colouring matter, as well as the chemical and

physical nature of the fabric--and it is so varied--will make such

classification, if it is to be thorough-going, not a very simple matter.

I may tell you that it is not a simple matter, and, moreover, the best

classification and arrangement is that one which depends both on the

action of the dyes on the fibres, and also on the intrinsic chemical

character of the dyestuffs themselves. Since the higher branches of

organic chemistry are involved in the consideration of the structure and

dispositions, and consequently more or less of the properties of these

dyes, you will readily comprehend that the thorough appreciation and use

of that highest and best method of classification, particularly in the

case of the coal-tar dyes, will be, more or less, a sealed book except

to the student of organic chemistry. But it may be asked, "How does that

highest and best method of classifying the dyestuffs affect the users,

the dyers, in their processes?" In reply, I would say, "I believe that

the dyer who so understands the chemical principles involved in the

processes he carries out, and in the best methods of classifying the

dyes as chemical substances, so as to be able to act independently of

the prescriptions and recipes given him by the dye manufacturers, and so

be master of his own position, will, _ceteris paribus_, be the most

economical and successful dyer." Many manufacturers of dyestuffs have

said the very same thing to me, but, independently of this, I know it,

and can prove it with the greatest ease. Let me now, by means of an

experiment or two, prove to you that at least some classification is

necessary to begin with. So different and varied are the substances used

as colouring matters by the dyer, both as regards their chemical and

physical properties, that they even act differently towards the same

fibre. I will take four pieces of cotton fabric; three of them are

simple white cotton, whilst the fourth cotton piece has had certain

metallic salts mixed with thickening substances like gum, printed on it

in the form of a pattern, which at present cannot readily be discerned.

We will now observe and note the different action on these pieces of

cotton--(i.) of a Turmeric bath, (ii.) a Magenta bath, and (iii.) a

madder or Alizarin bath. The Turmeric dyes the cotton a fast yellow, the

Magenta only stains the cotton crimson, and on washing with water alone,

almost every trace of colour is removed again; the madder, however,

stains the cotton with no presentable shade of colour at all, produces a

brownish-yellow stain, removed at once by a wash in water. But let us

take the printed piece of cotton and dye that in the Alizarin bath, and

then we shall discover the conditions for producing colours with such a

dyestuff as madder or Alizarin. Different coloured stripes are

produced, and the colours are conditioned by the kind of metallic salts

used. Evidently the way in which, the turmeric dyes the cotton is

different from that in which the madder dyes it. The first is a yellow

dyestuff, but it would be hard to assign any one shade or tint to

Alizarin as a dyestuff. In fact Alizarin (the principle of madder) is of

itself not a dye, but it forms with each of several metals a differently

coloured compound; and thus the metallic salt in the fabric is actually

converted into a coloured compound, and the fabric is dyed or printed.

The case is just the same with logwood black dyeing: without the

presence of iron ("copperas," etc.), sulphate of copper ("bluestone"),

or bichrome, you would get no black at all. We will now try similar

experiments with woollen fabrics, taking three simple pieces of flannel,

and also two pieces, the one having been first treated with a hot

solution of alum and cream of tartar, and the other with copperas or

sulphate of iron solution, and then washed. Turmeric dyes the first

yellow, like it did the cotton. Magenta, however, permanently dyes the

woollen as it did not the cotton. Alizarin only stains the untreated

woollen, whilst the piece treated with alumina is dyed red, and that

with iron, purple. If, however, the pieces treated with iron and alumina

had been dyed in the Magenta solution, only one colour would have been

the result, and that a Magenta-red in each case. Here we have, as proved

by our experiments, two distinct classes of colouring matters. The one

class comprises those which are of themselves the actual colour. The

colour is fully developed in them, and to dye a fabric they only require

fixing in their unchanged state upon that fabric. Such dyes are termed

_monogenetic_, because they can only generate or yield different shades

of but one colour. Indigo is such a dye, and so are Magenta, Aniline

Black, Aniline Violet, picric acid, Ultramarine Blue, and so on.

Ultramarine is not, it is true, confined to blue; you can get

Ultramarine Green, and even rose-coloured Ultramarine; but still, in

the hands of the dyer, each shade remains as it came from the

colour-maker, and so Ultramarine is a monogenetic colour. Monogenetic

means capable of generating one. Turning to the other class, which

comprises, as we have shown, Alizarin, and, besides, the colouring

principle of logwood (Hæmatein), Gallein, and Cochineal, etc., we have

bodies usually possessed of some colour, it is true, but such colour is

of no consequence, and, indeed, is of no use to dyers. These bodies

require a special treatment to bring out or develop the colours, for

there may be several that each is capable of yielding. We may consider

them as colour-giving principles, and so we term them _polygenetic_

colours. Polygenetic means capable of generating several or many. In the

various colours and dyes we have all phases, and the monogenetic shades

almost imperceptibly into the polygenetic. The mode of application of

the two classes of colours is, of course, in each case quite essentially

different, for in the case of the monogenetic class the idea is mainly

either to dye at once and directly upon, the unprepared fibre, or having

subjected the fabric to a previous preparation with a metallic or other

solution, to fix directly the one colour on that fabric, on which,

without such preparation, it would be loose. In the case of the

polygenetic class, the idea is necessarily twofold. The dyeing materials

are not colours, only colour generators. Hence in all cases the fabric

must be prepared with the twofold purpose--first, of using a metallic or

other agent, capable of yielding, with the dye material, the desired

colour; and secondly, of yielding it on the fibre in an insoluble and

permanent form. Now, though I have gone so far into this mode of

classification, because it does afford some information and light, yet I

can go no farther without getting into a territory that presupposes a

knowledge and acquaintance with the chemical structure of the colouring

matters as organic substances, which would be, at present, beyond us. I

shall now turn to another mode of classification, which, if not so

far-reaching as the other, is at least an exceedingly useful one. The

two methods may be combined to a considerable extent. By the latter plan

the colours may be conveniently divided into three groups: I.,

substantive colours; II., adjective colours; III., mineral and pigment

colours.

_Substantive Dyestuffs._--The substantive colours fix themselves readily

and directly on animal fibres and substances, but only a few amongst

them will dye vegetable fibres like cotton and linen directly. Almost

all substantive colours may, however, be fixed on cotton and linen by

first preparing or mordanting those vegetable fibres. Silk, wool, fur,

etc., act like fibre and mordant together, for they absorb and fix the

substantive colours firmly. In our experiments we saw that turmeric is

one of the few substantive colours fixing itself on both cotton and

wool, without any aid from a mordant or fixing agent. Magenta was also a

substantive colour, but Alizarin was certainly not one of this class.

_Adjective Dyestuffs._--Some of these substances are definitely coloured

bodies, but in some of them the colour is of no consequence or value,

and is quite different and distinct from the colour eventually formed on

the fibre, which colour only appears in conjunction with a special

mordant; but, again, some of them are not coloured, and would not colour

the fibre directly at all, only in conjunction with some mordant. All

the polygenetic colours are, of course, comprised in this class, for

example Alizarin and logwood (Hæmatein), whilst such monogenetic colours

as annatto and turmeric are substantive, for they will fix themselves

without a mordant on cotton and wool. The adjective colours can be

conveniently subdivided into--(_a_) those existing in nature, as logwood

(Hæmatein) and Cochineal; (_b_) those artificially formed from coal-tar

products, as Alizarin (madder), Gallein, etc.

_Mineral and Pigment Dyestuffs._--These colours are insoluble in water

and alcohol. They are either fixed on the fibre by mechanical means or

by precipitation. For example, you use blacklead or plumbago to colour

or darken your hats, and you work on this pigment colour by mechanical

means. I will show you by experiment how to fix a coloured insoluble

pigment in the fibre. I take a solution of acetate of lead (sugar of

lead), and to it I add some solution of bichrome (potassium bichromate).

Acetate of lead (soluble in water) with bichromate of potash (also

soluble in water) yields, on mixing the two, acetate of potash (soluble

in water), and chromate of lead, or chrome yellow (insoluble in water),

and which is consequently precipitated or deposited. Now suppose I boil

some of that chrome-yellow precipitate with lime-water, I convert that

chrome yellow into chrome orange. This, you see, takes place without any

reference to textile fibres. I will now work a piece of cotton in a lead

solution, so that the little tubes of the cotton fibre shall be filled

with it just as the larger glass tube or vessel was filled in the first

experiment. I next squeeze and wash the piece, so as to remove

extraneous solution of lead, just as if I had filled my glass tube by

roughly dipping it bodily into the lead solution, and then washed and

cleansed the outside of that tube. Then I place the fabric in a warm

solution of bichromate of potash (bichrome), when it becomes dyed a

chrome yellow, for just as chromate of lead is precipitated in the glass

tube, so it is now precipitated in the little tubes of the cotton fibre

(see Lecture I.). Let us see if we can now change our chrome yellow to

chrome orange, just as we did in the glass vessel by boiling in

lime-water. I place the yellow fabric in boiling lime-water, when it is

coloured or dyed orange. In each little tubular cotton fibre the same

change goes on as went on in the glass vessel, and as the tube or glass

vessel looks orange, so does the fabric, because the cotton fibres or

tubes are filled with the orange chromium compound. You see this is

quite a different process of pigment colouring from that of rubbing or

working a colour mechanically on to the fibre.

Let us now turn to the substantive colours (Group I.), and see if we can

further sub-divide this large group for the sake of convenience. We can

divide the group into two--(_a_) such colours as exist ready formed in

nature, and chiefly occur in plants, of which the following are the most

important: indigo, archil or orchil, safflower, turmeric, and annatto;

(_b_) the very large sub-group of the artificial or coal-tar colours. We

will briefly consider now the dyestuffs mentioned in Group (_a_).

_Natural Substantive Colours._--Indigo, one of the most valuable dyes,

is the product of a large number of plants, the most important being

different species of _indigofera_, which belong to the pea family. None

of the plants (of which _indigofera tinctoria_ is the chief) contain the

colouring matter in the free state, ready-made, so to say, but only as a

peculiar colourless compound called _indican_, first discovered by

Edward Schunck. When this body is treated with dilute mineral acids it

splits up into Indigo Blue and a kind of sugar. But so easily is this

change brought about that if the leaf of the plant be only bruised, the

decomposition ensues, and a blue mark is produced through separation of

the Indigo Blue. The possibility of dyeing with Indigo so readily and

easily is due to the fact that Indigo Blue absorbs hydrogen from bodies

that will yield it, and becomes, as we say, reduced to a body without

colour, called Indigo White, a body richer in hydrogen than Indigo Blue,

and a body that is soluble. If this white body (Indigo White) be exposed

to the air, the oxygen of the air undoes what the hydrogen did, and

oxidises that Indigo White to insoluble Indigo Blue. Textile fabrics

dipped in such reduced indigo solutions, and afterwards exposed to the

air, become blue through deposit in the fibres of the insoluble Indigo

Blue, and are so dyed. This is called the indigo-vat method. We can

reduce this indigo so as to prepare the indigo-vat by simply mixing

Indigo Blue, copperas (ferrous sulphate) solution, and milk of lime in a

closely-stoppered bottle with water, and letting the mixture stand. The

clear liquor only is used. A piece of cotton dipped in it, and exposed

to the air, quickly turns blue by absorbing oxygen, and is thus dyed.

The best proportions for the indigo-vat are, for cloth dyeing, 4000

parts of water, 40 of indigo, 60 to 80 of copperas crystals, and 50 to

100 of dry slaked lime. The usual plan is to put in the water first,

then add the indigo and copperas, which should be dissolved first, and

finally to add the milk of lime, stirring all the time. Artificial

indigo has been made from coal-tar products. The raw material is a

coal-tar naphtha called toluene or toluol, which is also the raw

material for saccharin, a sweetening agent made from coal-tar. This

artificial indigo is proving a formidable rival to the natural product.

Orchil paste, orchil extract, and cudbear are obtained by exposing the

plants (species of lichens) containing the colouring principle, called

_Orcin_, itself a colourless substance, to the joint action of ammonia

and air, when the oxygen of the air changes that orcin by oxidising it

into _Orcèin_, which is the true red colouring matter contained in the

preparations named. The lichens thus treated acquire gradually a deep

purple colour, and form the products called "cudbear." This dye works

best in a neutral bath, but it will do what not many dyes will, namely,

dye in either a slightly alkaline or slightly acid bath as well. Orchil

is not applicable in cotton dyeing. Being a substantive colour no

mordants are needed in dyeing silk and wool with it. The colour produced

on wool and silk is a bright magenta-red with bluish shade.

Litmus is also obtained from the same lichens as yield orchil. It is not

used in dyeing, and is a violet-blue colouring matter when neither acid

nor alkaline, but neutral as it is termed. It turns red with only a

trace of acid, and blue with the least trace of alkali, and so forms a

very delicate reagent when pieces of paper are soaked with it, and

dipped into the liquids to be tested.

Safflower: This vegetable dyeing material, for producing pink colours on

cotton without the aid of a mordant, consists of the petals of the

flower of _carthamus tinctorius_. It contains a principle termed

"Carthamin" or "carthamic acid," which can be separated by exhausting

safflower with cold acidulated water (sulphuric acid) to dissolve out a

yellow colouring matter which is useless. The residue after washing free

from acid is treated with a dilute solution of soda crystals, and the

liquid is then precipitated by an acid. A red precipitate is obtained,

which fixes itself directly on cotton thread immersed in the liquid, and

dyes it a delicate rose pink, which is, unfortunately, very fugitive.

Silk can be dyed like cotton. The colour is not fast against light.

Turmeric is the root portion of a plant called _curcuma tinctoria_, that

grows in Southern Asia. The principle forming the colouring matter is

"Curcumin." It is insoluble in cold water, not much soluble in hot, but

easily soluble in alcohol. From the latter solution it separates in

brilliant yellow crystals. Although the colour it yields is very

fugitive, the wool and silk dyers still use it for producing especially

olives, browns, and similar compound shades. It produces on cotton and

wool a bright yellow colour without the aid of any mordant. To show you

how easily dyeing with turmeric is effected, I will warm some powdered

turmeric root in a flask with alcohol, and add the extract to a vessel

of water warmed to about 140° F. (60° C.), and then dip a piece of

cotton in and stir it about, when it will soon be permanently dyed a

fine bright yellow. A piece of wool similarly worked in the bath is also

dyed. However, the unfortunate circumstance is that this colour is fast

neither to light nor alkalis. Contact with soap and water, even, turns

the yellow-dyed cotton, reddish-brown.

Annatto is a colouring principle obtained from the pulpy matter

enclosing the seeds of the fruit of a tree, the _Bixa orellana_, growing

in Central and Southern America. The red or orange colour it yields is

fugitive, and so its use is limited, being chiefly confined to silk

dyeing. The yellow compound it contains is called "Orellin," and it also

contains an orange compound called "Bixin," which is insoluble in water,

but readily soluble in alkalis and in alcohol with a deep yellow colour.

To dye cotton with it, a solution is made of the colour in a boiling

solution of carbonate of soda. The cotton is worked in the diluted

alkaline solution whilst hot. By passing the dyed cotton through water

acidulated with a little vitriol or alum, a redder tint is assumed. For

wool and silk, pale shades are dyed at 106° F. (50° C.) with the

addition of soap to the bath, dark shades at 200° to 212° F. (80° to

100° C.).

LECTURE X

DYESTUFFS AND COLOURS--_Continued_

_Artificial Substantive Dyestuffs._--You may remember that in the last

lecture we divided the colouring matters as follows: I. Substantive

colours, fixing themselves directly on animal fibres without a mordant,

only a few of them doing this, however, on vegetable fibres, like

cotton. We sub-divided them further as--(_a_) those occurring in nature,

and (_b_) those prepared artificially, and chiefly, but not entirely,

the coal-tar colouring matters. II. Adjective colours, fixing themselves

only in conjunction with a mordant or mordants on animal or vegetable

fibres, and including all the polygenetic colours. III. Mineral or

pigment colours. I described experiments to illustrate what we mean by

monogenetic and polygenetic colours, and indicating that the monogenetic

colours are mainly included in the group of substantive colours, whilst

the polygenetic colours are mainly included in the adjective colours.

But I described also an illustration of Group III., the mineral or

pigment colours, by which we may argue that chromate of lead is a

polygenetic mineral colour, for, according to the treatment, we were

able to obtain either chrome yellow (neutral lead chromate) or chrome

orange (basic lead chromate). I also said there was a kind of borderland

whichever mode of classification be adopted. Thus, for example, there

are colours that are fixed on the fibre either directly like indigo, and

so are substantive, or they may be, and generally are, applied with a

mordant like the adjective and polygenetic colours; examples of these

are Coerulein, Alizarin Blue, and a few more. We have now before us a

vast territory, namely, that of the _b_ group of substantive colours,

or, the largest proportion, indeed almost all of those prepared from

coal-tar sources; Alizarin, also prepared from coal-tar, belongs to the

adjective colours. With regard to the source of these coal-tar colours,

the word "coal-tar," I was going to say, speaks volumes, for the

destructive and dry distillation of coal in gas retorts at the highest

temperatures to yield illuminating gas, also yields us tar. But, coal

distilled at lower temperatures, as well as shale, as in Scotland, will

yield tar, but tar of another kind, from which colour-generating

substances cannot be obtained practically, but instead, paraffin oil and

paraffin wax for making candles, etc. Coal-tar contains a very large

number of different substances, but only a few of them can be extracted

profitably for colour-making. All the useful sources of colours and dyes

from coal-tar are simply compounds of carbon and hydrogen--hydrocarbons,

as they are called, with the exception of one, namely, phenol, or

carbolic acid. I am not speaking here of those coal-tar constituents

useful for making dyes, but of those actually extracted from coal-tar

for that purpose, _i.e._ extracted to profit. For example, aniline is

contained in coal-tar, but if we depended on the aniline contained ready

made in coal-tar for our aniline dyes, the prices of these dyes would

place them beyond our reach, would place them amongst diamonds and

precious stones in rarity and cost, so difficult is it to extract the

small quantity of aniline from coal-tar. The valuable constituents

actually extracted are then these: benzene, toluene, xylene,

naphthalene, anthracene, and phenol or carbolic acid. One ton of

Lancashire coal, when distilled in gas retorts, yields about 12 gallons

of coal-tar. Let us now learn what those 12 gallons of tar will give us

in the shape of hydrocarbons and carbolic acid, mentioned as extracted

profitably from tar. This is shown very clearly in the following table

(Table A).

The 12 gallons of tar yield 1-1/10 lb. of benzene, 9/10 lb. of toluene,

1-1/2 lb. of carbolic acid, between 1/10 and 2/10 lb. of xylene, 6-1/2

lb. of naphthalene, and 1/2 lb. of anthracene, whilst the quantity of

pitch left behind is 69-1/2 lb. But our table shows us more; it

indicates to us what the steps are from each raw material to each

colouring matter, as well as showing us each colouring matter. We see

here that our benzene yields us an equal weight of aniline, and the

toluene (9/10 lb.) about 3/4 lb. of toluidine, the mixture giving, on

oxidation, between 1/2 and 3/4 lb of Magenta. From carbolic acid are

obtained both Aurin and picric acid, and here is the actual quantity of

Aurin obtainable (1-1/4 lb.). From naphthalene, either naphthylamine (a

body like aniline) or naphthol (resembling phenol) may be prepared. The

amounts obtainable you see in the table. There are two varieties of

naphthol, called alpha- and beta-naphthol, but only one phenol, namely,

carbolic acid. Naphthol Yellow is of course a naphthol colour, whilst

Vermilline Scarlet is a dye containing both naphthylamine and naphthol.

You see the quantities of these dyes, namely 7 lb. of Scarlet and 9-1/2

lb. of the Naphthol Yellow. The amount of pure anthracene obtained is

1/2 lb. This pure anthracene exhibits the phenomenon of fluorescence,

that is, it not only looks white, but when the light falls on it, it

seems to reflect a delicate violet or blue light. Our table shows us

that from the 12 gallons of tar from 1 ton of coal we may gain 2-1/4 lb.

of 20 per cent. Alizarin paste. Chemically pure Alizarin crystallises in

bright-red needles; it is the colouring principle of madder, and also of

Alizarin paste. But the most wonderful thing about substantive coal-tar

colours is their immense tinctorial power, _i.e._ the very little

quantity of each required compared with the immense superficies of cloth

it will dye to a full shade.

TABLE A.[2]

-------------------------------------------------------------------------------

TWELVE GALLONS OF GAS-TAR

(AVERAGE OF MANCHESTER AND SALFORD TAR) YIELD:--

---------+---------+------+----------+----+--------------+---+---+--------+----

Benzene.| Toluene.| P |Solvent | H N| Naphthalene. | C | H | A | P

| | h |Naphtha | e a| | r | e | n | i

| | e |for | a p| | e | a | t | t

| | n |India | v h| | o | v | h | c

| | o |rubber, | y t| | s | y | r | h

| | l |containing| h| | o | | a | .

| | . |the three | a| | t | O | c |

| | |Xylenes. | .| | e | i | e |

| | | | | | . | l | n |

| | | | | | | . | e. |

---------+----------------+----------+----+--------------+---+---+-------------

1·10 lb.=|0·90 lb.=|1·5 |2·44 lb., |2·40|6·30 lb. = |17 |14 |0·46 lb.|69·6

1·10 lb. |0·77 lb. |lb. |yielding |lb. |5·25 lb. of |lb.|lb.|= 2·25 | lb.

of | of |= 1·2 |0·12 lb. | |alpha- | | | lb. of |

| |Aurin.|= 0·07 lb.| |= 7·11 lb. of | | | (20%). |

| | |of | |Vermilline | | | |

or 1·10 | | | | |or beta- | | | |

1·23 lb. | | | | |Yellow | | | |

---------+---------+------+----------+----+--------------+---+---+--------+----

[Footnote 2: This table was compiled by Mr. Ivan Levinstein, of

Manchester.]

The next table (see Table B) shows you the dyeing power of the colouring

matters derived from 1 ton of Lancashire coal, which will astonish any

thoughtful mind, for the Magenta will dye 500 yards of flannel, the

Aurin 120 yards, the Vermilline Scarlet 2560 yards, and the Alizarin 255

yards (Turkey-red cotton cloth).

The next table (Table C) shows the latent dyeing power resident, so to

speak, in 1 lb. of coal.

By a very simple experiment a little of a very fine violet dye can be

made from mere traces of the materials. One of the raw materials for

preparing this violet dye is a substance with a long name, which itself

was prepared from aniline. This substance is

tetramethyldiamidobenzophenone, and a little bit of it is placed in a

small glass test-tube, just moistened with a couple of drops of another

aniline derivative called dimethylaniline, and then two drops of a

fuming liquid, trichloride of phosphorus, added. On simply warming this

mixture, the violet dyestuff is produced in about a minute. Two drops of

the mixture will colour a large cylinder of water a beautiful violet.

The remainder (perhaps two drops more) will dye a skein of silk a bright

full shade of violet. Here, then, is a magnificent example of enormous

tinctorial power. I must now draw the rein, or I shall simply transport

you through a perfect wonderland of magic, bright colours and apparent

chemical conjuring, without, however, an adequate return of solid

instruction that you can carry usefully with you into every-day life and

practice.

TABLE B.[3]

-------------------------------------------------------------------------------

DYEING POWERS OF COLOURS FROM 1 TON OF LANCASHIRE COAL.

------------+------------+------------+-------------+-------------+------------

yards of |dye 1000 |dye 3800 |yards of |yards of |dye 255

------------+------------+------------+-------------+-------------+------------

TABLE C.[3]

-------------------------------------------------------------------------------

DYEING POWERS OF COLOURS FROM 1 LB. OF LANCASHIRE COAL.

------------+------------+------------+-------------+-------------+------------

Methyl | Naphthol Vermilline | Aurin | Alizarin

Magenta or Violet. | Yellow. or Scarlet. | (Orange). |(Turkey Red)

------------+------------+------------+-------------+-------------+------------

8 × 27 |24 × 27 |61 × 27 |41 × 27 |1·93 × 27 |4 × 27

------------+------------+------------+-------------+-------------+------------

[Footnote 3: These tables were compiled by Mr. Ivan Levinstein, of

Manchester.]

Before we go another step, I must ask and answer, therefore, a few

questions. Can we not get some little insight into the structure and

general mode of developing the leading coal-tar colours which serve as

types of whole series? I will try what can be done with the little

knowledge of chemistry we have so far accumulated. In our earlier

lectures we have learnt that water is a compound of hydrogen and oxygen,

and in its compound atom or molecule we have two atoms of hydrogen

combined with one of oxygen, symbolised as H_{2}O. We also learnt that

ammonia, or spirits of hartshorn, is a compound of hydrogen with

nitrogen, three atoms of hydrogen being combined with one of nitrogen,

thus, NH_{3}. An example of a hydrocarbon or compound of carbon and

hydrogen, is marsh gas (methane) or firedamp, CH_{4}. Nitric acid, or

_aqua fortis_, is a compound of nitrogen, oxygen, and hydrogen, one atom

of the first to three of the second and one of the third--NO_{3}H. But

this nitric acid question forces me on to a further statement, namely,

we have in this formula or symbol, NO_{3}H, a twofold idea--first, that

of the compound as a whole, an acid; and secondly, that it is formed

from a substance without acid properties by the addition of water,

H_{2}O, or, if we like, HOH. This substance contains the root or radical

of the nitric acid, and is NO_{2}, which has the power of replacing one

of the hydrogen atoms, or H, of water, and so we get, instead of HOH,

NO_{2}OH, which is nitric acid. This is chemical replacement, and on

such replacement depends our powers of building up not only colours, but

many other useful and ornamental chemical structures. You have all heard

the old-fashioned statement that "Nature abhors a vacuum." We had a very

practical example of this when in our first lecture on water I brought

an electric spark in contact with a mixture of free oxygen and hydrogen

in a glass bulb. These gases at once united, three volumes of them

condensing to two volumes, and these again to a minute particle of

liquid water. A vacuum was left in that delicate glass bulb whilst the

pressure of the atmosphere was crushing with a force of 15 lb. on the

square inch on the outside of the bulb, and thus a violent crash was the

result of Nature's abhorrence. There is such a kind of thing, though,

and of a more subtle sort, which we might term a chemical vacuum, and it

is the result of what we call chemical valency, which again might be

defined as the specific chemical appetite of each substance.

The Chemistry of Hat Manufacturing Lectures Delivered Before the Hat Manufacturers' Association · 第 6 / 11 段

_Classification._--In classifying the different dyestuffs and colouring