It has been our custom for thirty years past to devote a considerable
space to the answering of questions by correspondents; so useful have
these labors proved that the SCIENTIFIC AMERICAN office has become the
factotum, or headquarters, to which everybody sends, who wants special
information upon any particular subject. So large is the number of our
correspondents, so wide the range of their inquiries, so desirous are
we to meet their wants and supply correct information, that we are
obliged to employ the constant assistance of a considerable staff of
experienced writers, who have the requisite knowledge or access to
the latest and best sources of information. For example, questions
relating to steam engines, boilers, boats, locomotives, railways,
etc., are considered and answered by a professional engineer of
distinguished ability and extensive practical experience. Inquiries
relating to electricity are answered by one of the most able and
prominent practical electricians in this country. Astronomical queries
by a practical astronomer. Chemical inquiries by one of our most
eminent and experienced professors of chemistry; and so on through
all the various departments. In this way we are enabled to answer the
thousands of questions and furnish the large mass of information which
these correspondence columns present. The large number of questions
sent--they pour in upon us from all parts of the world--renders it
impossible for us to publish all. The editor selects from the mass
those that he thinks most likely to be of general interest to the
readers of the SCIENTIFIC AMERICAN. These, with the replies, are
printed; the remainder go into the waste basket. Many of the rejected
questions are of a primitive or personal nature, which should be
answered by mail; in fact, hundreds of correspondents desire a special
reply by post, but very few of them are thoughtful enough to inclose
so much as a postage stamp. We could in many cases send a brief reply
by mail if the writer were to inclose a small fee, a dollar or more,
according to the nature or importance of the case. When we cannot
furnish the information, the money is promptly returned to the sender.
J. P. D. will find directions for colored whitewash on pp. 235, 236,
vol. 36.--A. M. will find directions for electroplating on p. 59, vol.
36.--H. P. can recover silver from photographers' waste by the process
detailed on p. 250, vol. 27.--A. W. A.'s difficulty as to 64 and 65
squares in the puzzle can be solved by an inspection of the diagrams
on p. 323, No. 21, SCIENTIFIC AMERICAN SUPPLEMENT.--I. A. will find a
description of a magneto-electric machine on p. 195, vol. 34. A clock
thus would go for 12 hours, and wind itself at the same time for
12 hours more, if such a machine could exist, would be a perpetual
motion. As to tempering small drills, see p. 186, vol. 26.--R. B. can
prevent rust on iron or steel by the means described on p. 26, vol.
25. For a recipe for a depilatory, see p. 186, vol. 34.--A. T. R. is
informed that the hydrocarbon engine is reversible.--T. W. will find
directions for making sand belts on p. 235, vol. 36.--M. G. should
address a manufacturer of oxygen cylinders.--J. S. C., who inquires
as to a water fountain, sizes of pipes, etc., should send us a sketch
with dimensions.--O. L. is informed that the proper way to ascertain
the relative strengths of corrugated and plain sheet metal is by
experiment.--G. H. B. will find directions for making colored
printing inks on p. 90, vol. 36.--P. M. will find on p. 250, vol. 36,
directions for making a polishing starch.--C. H. B. can braze the ends
of his brass plate to make a cylinder of it. See p. 219, vol. 36.--W.
H. C. is informed that his method of fluting reamers is not
new.--C. C. G. will find his method of raising coal or other weights
impracticable.--E. S. G. had better test so simple an experiment and
satisfy himself.--W. H. C. is informed that the most satisfactory plan
would be to get his tools nickel-plated.
(1) J. H. N., of Christ Church, New Zealand, asks: Is the stearin from
which the olein has been extracted by Dr. Mott's process fit to be
made at once into good stearin candles, without any further treatment?
A. Yes.
(2) B. B. says: I wish to express the strongest coloring matter from
certain herbs, sage leaves, for instance. How can it best be done
cheaply and quickly? Evaporation during several days, after boiling
and simmering, has the effect; but it is inconveniently slow. The
color produced is a medium brown. A. Dry the leaves, etc., thoroughly,
and grind to a fine powder. Digest this for several days in enough
warm water to thoroughly moisten it throughout. Then add enough wood
naphtha to make a stiff paste, and after standing an hour transfer to
a fine linen bag and express the thick liquid in a screw press. 2. Is
there anything that will set the color? A. Try a strong hot solution
of alum.
(3) H. K. F. M. says: I have a box made of Bohemian crystal. The
cover, which was held to the box by a brass frame, has come apart
from its frame. It seemed to have been cemented by a hard substance
resembling plaster of Paris. How can I make it? A. Boil 3 parts
powdered rosin for sometime with 1 part of caustic soda and 5 parts of
water; then stir into the soap formed one half its weight of plaster
of Paris, and use immediately.
(4) F. N. Y. asks: Would a canvas bag, coated with a varnish made of
india rubber dissolved in naphtha, be suitable to hold oxygen gas? A.
Yes; but bags made of double pieces of cloth, cemented together with
the varnish, are better.
(5) J. A. B. asks: Is there any difference between electricity
and magnetism? A. Electricity and magnetism are supposed to be
manifestations of the same force whose actions are produced at
right angles to each other; the action which occurs in the line of
polarization being called electricity, and the one at right angles to
this line, magnetism. There is an important difference between
them, however, as electricity is essentially a dynamic force, while
magnetism is purely static.
1. Is not the idea of the world moving around the sun in an elliptic
form absurd? A. No. 2. My idea is that the north star is the center
of the universe, or in fact is the magnet that all the suns or fixed
stars move around, and that the attraction of the pole of the earth,
although it moves around the sun, is the cause of the change of
seasons, or, in other words, the angle of light. A. There is nothing
whatever to support the idea. But a supposed center of the universe
has really been designated by some astronomers.
(6) P. S. asks: How much copper wire does it require to construct an
electro-magnet that will uphold 100 lbs., and what size of wire should
be used? A. Probably 500 or 600 feet of No. 14 copper wire would be
sufficient with 3 or 4 very large size Grove cells and cores about 6
inches long and 1 inch in diameter.
(7) H. S. B. says: Water falls about 16 feet per second. My overshot
water wheel moves about 4 feet per second. Do I in that way lose that
percentage of the actual power of the water? A. Not necessarily.
(8) C. N. B. asks: Can a steam engine be worked with compressed air
the same as with steam? A. Generally speaking, it can; but not in
every respect.
(9) J. Y. says: If all the measures of length, surface, and capacity
in the world, and all the weights were lost, by what means could new
ones be made corresponding exactly with those we now have? A. It would
be impossible, as all the measures in use refer to certain arbitrary
standards.
(10) R. B. G. asks: If a horse be pulling at the end of a lever and
traveling 3 miles an hour, how many lbs. pressure against his collar
must he exert, to raise 33,000 lbs. 1 foot per minute? A. The force
exerted by the animal will depend upon the length of the lever, which
should be given.
(11) C. H. McK. asks: Would a pump so constructed as to create an
incessant suction draw water an indefinite distance, or how far would
it draw it? A. Such a pump would raise water no higher than any other
that was equally tight.
(12) J. W. says: I wish to get some boilers made about 12 inches
in diameter and 13 inches deep. I want them to stand a pressure
corresponding to 400 deg. Fah deg.. Do you think it would be safe to have them
made of cast iron? A. We think it will be better to use wrought iron.
Make the shell about 7/16 of an inch thick.
(13) J. R. S. says, in reply to E. W. P., who says that he has
an artesian well which does not flow; but from which he pumps by
inserting a pipe inside the well tubing, and asks: "If we attach the
pump to the well tubing directly, allowing no air to enter the tube,
would it not be like trying to pump water from an airtight barrel?" If
such were the case, the drive well would be a miserable failure; for
in all drive wells the pump is attached directly to the tube. I would
advise E. W. P. to attach his pump to the well tube direct, and he
will gain three times the amount of water that he now gets. By having
his pump attached to the well tube directly, the working of the pump
creates a vacuum, and the atmospheric pressure on the earth's surface
violently forces the liquid to fill the vacuum thus formed, thereby
giving a much greater amount of water than can be otherwise obtained.
It is a well established fact that more water can be obtained by the
drive well than by any other. A. In our answer to E. W. P., it will
be evident, we think, to most of our readers, that we only referred to
the case in which the well had no connection with the atmosphere, when
the pipe was tightly fitted. It appears, however, that it might have
been better to have stated this more definitely, and we gladly
embrace the opportunity afforded by the interesting letters of
our correspondents. We would be glad to receive from J. R. S. some
experimental data in proof of his assertion as to the great gain from
a tight connection. This also answers J. T. G. and W. H. F.
(14) H. H. S. says: 1. Given, a boat with a 35 feet keel, of 6 feet
beam, with fine lines; also a two-cylinder engine, each cylinder 4 x
5 inches; and a wheel 28 inches in diameter and of 31/2 feet pitch. Will
an upright boiler, with 135 square feet heating surface, and 4 square
feet grate surface, be sufficient to run the engine at 250 or 300
revolutions per minute with 100 lbs. steam? A. With good coal and
a forced draft, the boiler may be large enough. 2. What will be the
probable speed of boat? A. In smooth water, 7 to 8 miles an hour.
(15) F. A. asks: What would be a safe outside pressure for a cylinder
of wrought iron, 1/2 inch thick and 4 feet in diameter, and 8 feet long?
A. According to tables given in Wilson's "Treatise on Steam Boilers,"
the working pressure for such a tube would be about 65 lbs. per square
inch.
(16) F. M. M. asks: 1. How large must an engine be to run a boat 121/2
feet wide, 75 feet long, drawing 4 feet of water, at the rate of 30
miles per hour, on a river or bay where the surface is smooth? A. We
have some doubts as to whether these conditions could be fulfilled. 2.
Do steamboats on the ocean use salt water in their boilers for
steam, or do they carry fresh water? A. They ordinarily have surface
condensers, so that the water of condensation is returned to the
boilers.
(17) E. S. N. says: Please give your ideas as to how much water an
engine 18 inches in diameter by 22 inches stroke, running at 145
revolutions per minute, at 80 lbs. steam, cutting off at about 18
inches, will require. We furnished an injector for one of the above
dimensions, capable of throwing 900 gallons per hour. It was found
to be insufficient, and I went to the mill to discover the cause, if
possible. The manufacturers of the injector thought it ought to be
large enough, and so did we. I found everything set up properly, and
the piston and valve were evidently in good order. I finally measured
the capacity of the tank which supplied the injector, and found
that it drew 960 gallons per hour. A. We do not think the data are
sufficient for an accurate calculation. It is possible, however, that
some of our readers have made experiments on similar engines, and can
give some useful information.
(18) T. W. asks: What size of breast water wheel, with a fall of 2
feet water, would it require to produce the same power as an overshot
wheel of 4 feet diameter, 18 inches face, with a fall of 5 feet water?
A. If the breast wheel gave the same efficiency as the other, it would
require a face about 21/2 times as wide.
(19) A. K. says: A. asserts that if a small and a large boiler be set
side by side and connected with the top gauge cock of the two boilers,
level, when they are first filled with water, and then steam is
raised, that the water will not remain the same, that the pressure
will be greater in the larger boiler, and consequently will force the
water into the smaller one. B. says that the water will always remain
the same as long as the boilers are connected; that the pressure on
the water will be the same in both boilers, and therefore the water
will always assume the same level in each. Which is right? A. The
pressures sometimes vary in two boilers connected in this way; and
they should be set in such a way that the water cannot be forced from
one into the other under any circumstances.
(20) J. T. G. says: I notice your reply to W. G. in regard to pounding
of a steam pump, in which you recommend the use of a larger air
vessel. I think that W. G. can remedy the difficulty by allowing a
small quantity of air to enter the pump cylinder at each stroke,
which can be done without sensibly diminishing the amount of water
delivered, provided the lift is not so high as to nearly equal the
capacity of the pump. That would keep the maximum quantity of air in
the air vessel, and I think that the air in the discharge pipe would
have the effect of converting a comparatively rigid column into an
elastic one. W. G. can easily try the experiment by running with
the drain cocks at the end of his pump partially open; and if that
remedies the difficulty, he might insert a small check valve opening
inward to prevent the discharge of water during the out-stroke. If W.
G. tries this, I wish that he would let us know the result through the
SCIENTIFIC AMERICAN.
(21) G. H. says: Please decide the following: A. claims that a team
of horses can draw a greater load when hitched close to it than when
hitched at a distance of 10 or 20 feet. B. claims that, everything
else being equal, distance makes no difference, and that the team
could pull as many lbs. at a distance of 20 feet as it could at ten or
less. Which is right? A. We incline to B.'s opinion.
Please tell me the relative power of conducting electricity of
the principal metals. A. According to Matthiessen, the electrical
conductivity of the principal metals, under similar conditions, is as
follows:
Silver 100.0
Copper 99.9
Gold 80.0
Aluminium 56.0
Sodium 37.4
Zinc 29.0
Cadmium 23.7
Potassium 20.8
Platinum 18.0
Iron 16.8
Tin 13.1
Lead 8.3
German silver 7.7
Antimony 4.6
Mercury 1.6
Bismuth 1.2
(22) S. R. S. asks: How can lime, or rather phosphate of lime, be
precipitated from cod liver oil, which is perfectly clear and said to
contain 2 per cent. of the phosphate? A. This can only be done by
first destroying the organic matter of the oil, and then examining the
residue for the phosphates with the usual reagents--magnesia solution,
barium chloride, nitrate of silver, ammonium molybdate, etc. With so
small a percentage of the phosphates, it will be necessary for you to
work with concentrated solutions, and slowly. The oil may be oxidized
by treating it on the waterbath with hot hydrochloric acid, with
some chlorate of potash, added in small quantities at a time. Then
evaporate down nearly to dryness, and treat with a little strong
nitric and a few drops of sulphuric acid. This will take some time if
properly done.
(23) J. H. S. says, in answer to J. H. B.'s query as to a parrot
pulling out his feathers: Take a knife and scrape the inside edge of
the bill, and the feathers will slip from the bill without coming out.
This is done for feather-eating hens; no doubt it will answer for a
parrot as well.
(24) S. R. S. says: I have some dentists' pellet gold. I alloyed it
with brass and silver. I melted it several times, but it was so very
brittle that I could not work it. I then added a $21/2 gold coin, and
fused, all together, but it was as brittle as before. I then fused it
and dropped in lumps of pure saltpeter, but it is still as brittle
as before. I fused the gold on a lump of charcoal with an alcohol
blowpipe. Please tell me how to work it. A. You fail to state the
proportions of your alloy. There may be an excess of zinc and copper,
or the fusion may not have been complete. Place it, together with
several small pieces of rosin and a little borax or carbonate of soda,
in a small blacklead crucible, and heat to very bright redness over
a good fire. If this does not obviate the difficulty, fuse the alloy
with about three times its weight of nitrate of potassa (saltpeter),
and treat the mass when cold with dilute sulphuric acid. Pour off the
acid solution and fuse the alloy, together with any silver sulphate
adhering to it and a little carbonate of soda. Any silver contained in
the acid solution may be recovered by adding a little salt or muriatic
acid, and fusing the precipitated chloride of silver with carbonate of
soda.
(25) N. S. asks: 1. Can water be decomposed into its constituents
(oxygen and hydrogen) with any considerable rapidity, and in large
quantities, by electricity? A. Yes; providing a large magneto-electric
machine be used. 2. What is the best and cheapest method of generating
hydrogen in large quantities? A. The action of iron or zinc scraps
on diluted oil of vitriol is among the best. A considerable volume
of pure hydrogen may also be obtained with facility by passing
superheated steam through a large iron tube filled with scrap iron
heated to bright redness.
(26) G. S. D. W. asks: Is there any process by which an engraving can
be transferred either to stone or wood, where the printing ink can
be made to show up as black as in the original after the transfer has
been made? A. We know of no satisfactory method whereby this may
be accomplished directly. By means of the chromate of gelatin
photographic process, such transfers may be made without great
difficulty.
(27) F. M. M. asks: 1. If a steamboat 100 feet long, of 5 feet beam
and 4 feet draught, be provided with one set of common side paddle
wheels, and power enough to run it at the rate of 10 knots per
hour, would two sets of side wheels, with the power doubled and the
revolutions of the wheels doubled, double the speed of the boat? A.
No. 2. If we take the same boat, side wheels, and power, for running
10 knots per hour, and arrange for the side wheels to feather their
paddles, what effect would it have on the speed of the boat? A. You
might obtain from 10 to 15 per cent. more of the power of the engine in
useful effect.
(28) W. J. T. asks: 1. What is the best dark color to paint a
laboratory, and what kind of paint must I use? A. One of the best for
this purpose is shellac in alcohol, colored to suit with Vandyke or
Spanish brown, etc. 2. I wish to varnish my benches. What varnish
would you recommend? A. Shellac is commonly used, but copal gives good
results, also Brunswick black in oil.
Of what should a waste water pipe be made, so as to resist acids? A.
Make it of lead or block tin.
Can you recommend an elementary work on electric batteries? A.
Sprague's "Electricity: its Theory, Sources, and Applications," is one
of the best.
(29) T. P. H. asks: Can I take a wax impression off type and then
electrotype it with a battery? A. Yes. This is the common method of
making electrotypes for printing from.
(30) C. M. asks: What are the locations of the various branch mints of
the United States? A. A recent authority gives them as Philadelphia,
Pa., San Francisco, Cal., Carson City, Nev., and Denver, Col. Assay
offices are situated at New York city, Charlotte, N. C., and Boise
City, Idaho.
(31) B. L. D. asks: Can you give me a recipe for making paste for
sharpening razors, knives, etc.? A. Mix the finest emery obtainable
with a little suet.
(32) C. B. McM. says: I hear that four gallon measures of different
capacities are in use, and that The United States standard gallon
contains 230 cubic inches. In the confusion of text-book statements
such as--"wine gallon = 231 cubic inches," "beer gallon = 282 cubic
inches," "American standard gallon = 58973 grains (Youmans' Chemistry)
= nearly 234 cubic inches," and the very extensive ignorance of what
is really correct, please repeat the information in a way that may
be quoted as authority for the capacity of a United States gallon in
cubic inches, and the weight in grains. A. "The gallon of the United
States is the standard or Winchester wine gallon of 231 cubic inches,
and contains 8.3388822 lbs. avoirdupois, or 58372.1754 troy grains of
distilled water at 39.83 deg. Fah., the barometer being at 30 inches. It
is equal to 3.785207 liters. The gallon of the State of New York is of
the capacity of 8 lbs. pure water at its maximum density, or
221.184 cubic inches. It is equal to 3.62346 liters."--_Appleton's
Cyclop[oe]dia._
(33) S. C. D. says: Please give directions for electrotyping
cylindrical rollers for impressing upon sheets of wax, accurately,
of the proper figure for honeycomb foundations. The figure for the
surface of the cylinders to be derived from sheets of wax foundation,
having the figure correctly impressed upon them. A. This can be done
by coating with plumbago, and then electrotyping with copper, in a way
familiar to most printers and to all electrotyping establishments. The
plates can afterwards be bent round a roller, and used to impress the
sheets of wax.
(34) J. H. T. asks: There is a piece of ground, 100 rods long and 10
rods wide at one end, running to a point at the other, which we wish
to divide into 4 equal lots. Please give a rule. A. Let the 100 rods
be the base of a triangle, divide it into 4 parts of 25 rods each, and
join the apex with each of the three dividing points. You will then
have 4 triangles on equal bases and between the same parallels, which,
according to Euclid, are equal to each other.
(35) R. S. asks: What are the chemical qualities of bisulphide
of lime, and how can I prepare it? A. The bisulphide of calcium
(C_{2}S_{5}) is produced by boiling milk of lime with sulphur and
water, but not long enough to allow the lime to become completely
saturated. The filtered liquid, on cooling, deposits crystals whose
composition agrees with the formula C_{2}S_{2} + 3H_{2}O. Exposed to
the air, it soon absorbs oxygen, becoming converted into insoluble
sulphate of calcium. Its aqueous solutions are likewise decomposed.
Its reactions with the metallic salts are similar to those of the
alkaline sulphides.
(36) H. M. S. asks: 1. Of what is the bronze preparation made and how
is it applied to clock fronts? A. Bronze powders are made of various
metallic alloys. The gold bronze is usually made of Dutch gold
(an alloy of copper and zinc) and of the bisulphide of tin (_aurum
musivum_). They are usually applied to metal work by means of an oil
size or japan varnish. 2. In what way can I remove the old bronze? A.
Wash first with a solution of washing soda (hot), clean and dry, and
then rub with a little benzole, alcohol, or ether.
(37) W. E. W. asks: 1. Of what mixture is the bright red paint usually
put upon axes made? A. It consists of fine vermilion ground with
1 part boiled oil and 2 parts turpentine. 2. Is more than one coat
applied? A. One coat will suffice. It is best applied with a fine
brush, when the metal is warm.
(38) C. M. B. asks: Is the odor emitted by the ailanthus tree
unwholesome? A. It is considered so by many, but we have no proof as
to the facts.
(39) L. S. & Co. ask: Is there anything known which would clean the
hands from paints and lacquers without the use of turpentine? A. A
little ammonia and benzine or naphtha, aided by a little sand, is
often used in stubborn cases; put plenty of good soap and warm water,
with a stiff brush or a small piece of pumicestone, will ordinarily
suffice.
(40) W. P. S., Jr., says: Can you give me a recipe for making _papier
mache_? A. _Papier mache_ is obtained from old paper and the like made
into a pulp by grinding with milk of lime or lime water, and a little
gum dextrin or starch. This pulp is then pressed into form, coated
with linseed oil, baked at a high temperature, and finally varnished.
The pulp is sometimes mixed with clay (kaolin), chalk, etc.; and other
kinds are made of a paste of pulp and recently slaked lime. This is
used for ornamenting wood, etc.
(41) M. P. B. says, in reply to a correspondent who asked how to
prevent his water filter from getting choked up: Fit in the filter,
on the top of the charcoal, a piece of board having in the center a
circular hole from two to four inches in diameter, according to the
size of the filter; force in this a sponge so tightly that all the
water has to pass through it first, but not so as to prevent its free
passage. This sponge will absorb readily the gross impurities of the
water, and can easily be taken out and cleaned once or twice a week.
(42) A. C. S. asks: 1. Is there any reason why lightning rod points
should always be bright, if the points are kept sufficiently sharp? A.
It makes no difference if the points are not bright. 2. If lightning
rods put up in the ordinary way above the roof terminate in the eaves'
spouting of the house, and said spouting had good ground connections,
would this not be equal to the best lightning rod, and thereby save
many feet of rod and many dollars of expense? A. The arrangement you
suggest would be good. Make a thoroughly good ground connection with
leaders, have all joints well soldered, and you may dispense with the
rod as you propose.
(43) J. A. W. says: Having occasion to do some copper plating some
time ago, I dissolved sulphate of copper in water in a glass jar. I
then poured it off into my battery, and there was some left in the
jar. I threw a small piece of iron into it and left it for some days.
I then took it out; and to my surprise, I found that it had been
perfectly plated with copper. Please let me know the cause? A. The
reaction you note is taken advantage of to cheaply copper plate small
articles of cast iron. See answer to J. O. M., p. 347, vol. 36. In the
presence of water, the reaction is as follows:
CuSO_{4} + Fe = FeSO_{4} + Cu.
Sulphate of copper. Iron. Sulphate of iron. Copper.
As the iron is a more positive metal than copper, it displaced the
latter in combination with acids, the remaining portions of the iron
becoming coated with the precipitated copper.
(44) A. G. asks: Is the silver, for a reflecting telescope, put on the
back of the glass the same as on looking glasses? A. No. Only one
side of the glass is ground and polished to the shape required. The
silvering is done on this side; and then, with the softest buckskin
and the finest rouge, the surface of the silver is polished for the
reflecting surface. In cities where gas is used, it will not retain
its brilliancy very long; then it requires to be cleaned with nitric
acid and resilvered, which is only the work of a few hours when a
person has become accustomed to it.
(45) A. L. B. says: 1. I understand that, in modern chemistry, the
acids and alkalies are the two extremes of a class of substances
called hydrates, the only difference being the radical. In the
reaction of nitric acid, HO NO_{2} or HNO_{3} on potassic hydrate, KOH
is KO NO_{2} or KNO_{3}, and H_{2}O. Which molecule loses the oxygen
atom, and why should one part with it more than the other?
A. HNO_{3} + KOH = KNO_{3} + H_{2}O
Nitric acid potassic potassic water
hydrate nitrate
In this reaction the potassium is considered, by virtue of its greater
affinity, as replacing the hydrogen atom in the hydric nitrate; the
hydrogen in turn satisfying the OH group to form water. These hydrates
are similar only in point of constitution. Their chemical deportments
are widely different. 2. What are oxides in modern chemistry? A. The
bodies formed by the direct combination of oxygen with the elementary
bodies are called oxides. With water some of these oxides form
hydrates, as
K_{2}O + H_{2}O = 2(KHO)
potassium water potassic
oxide hydrate
(46) J. R. M. asks: To have a circular saw run well, should the
mandrel have a little end play if it is desired to relieve the saw
and guides of strain? A. If the saw is not true or the carriage runs
crooked, end play of the mandrel to the extent of the deviations will
relieve the strain upon the saw. But if the carriage runs true and the
saw true, the mandrel should have no end play.
MINERALS, etc.--Specimens have been received from the following
correspondents, and examined, with the result stated:
M. S. M.--It is a quartz crystal, the opposite sides of which
have been ground flat, probably by artificial means.--F. B.--It is
graphite.
* * * * *