Page images


Centrifugal Force Problem

ured in the same units, represents the What is the centrifugal force of a forty- proportion of voids. The proportion of pound weight revolving seventy-five times per

voids in sand may be more accurately deminute, when it is suspended three feet from the center of a shaft?-G. D. H.

termined by subtracting the weight of a

cubic foot of packed sand from 165, the To find the centrifugal force of a given

weight of a cubic foot of quartz, and diweight, multiply the square of the revo

viding the difference by 165. lutions per minute by the radius of the

The following will serve as an example circle, in feet, in which the weight re

of proportioning materials: Assume volves, and this product by the weight

egint voids in packed sand to measure 38 per itself. This last product multiplied by

cent., and voids in packed stone to measure 48 per cent. Cement paste required per cubic foot of sand, 0.38 and 1-10 equals 0.42 cubic foot, approximately. By trial, one cubic foot of loose cement, lightly shaken makes 0.85 cubic foot of cement paste, and requires 0.39 or two cubic feet of sand, approximately producing an amount of mortar equal to 0.85 and 2 (1-0.38) equals 2.09 cubic feet. Mortar required per cubic foot of stone equals 0.48, and 1-10x0.48 equals 0.528 cubic foot. Therefore 2.09 cubic feet mortar will require 5.69% equals four cubic feet of stone, approximately. The

proportions are therefore one part ce- - - S S -

ment, two parts sand, four parts stone.

Although such a determination is usually CENTRIFUGAL FORCE PROBLEM Diagram.

considered unnecessary in practical work,

it may be of sufficient interest to justify the constant, .000341, will give the cen- giving it. trifugal force in terms of the weight of For general use the following mixtures the body. 752x3x40x.000341=230.175 are recommended: One cement, two pounds.-Ans.

sand, four aggregate, for very strong and impervious; one cement, two and one

half sand, five aggregate, for ordinary Mixing Concrete

work requiring moderate strength; one How are the materials for concrete proportioned ?-D. O. F.

cement, three sand, six aggregate, for

work where strength is of minor imFor an accurate determination of the

1. the portance. best and most economical proportions where maximum strength is required, it

Value of Algebra is well to proceed in the following way:

e Tonowing way: Please tell me the advantages of Algebra to First, proportion the cement and sand so a Draughtsman or Engineer.-A. R. T.. that the cement paste will be 100 per In algebra numbers are expressed by cent in excess of the voids in sand ; next, the letters of the alphabet; the advantage determine the voids in the aggregate and of the substitution is that we are enabled allow sufficient mortar to fill all voids to pursue our investigations without bewith an excess of 10 per cent.

ing embarrassed by the necessity of perTo determine roughly the voids in forming arithmetical operations at every gravel or crushed stone, prepare a water- step. tight box of convenient size and fill with Thus, if a given number be represented the material to be tested, shake well and by the letter a, we know that 2a will repsmooth off even with the top. Into this resent twice that number, and a the pour water until it rises flush with the half of that number, whatever the value surface. The volume of water added di- of a may be. In like manner if a be vided by the volume of the box, meas- taken from a there will be nothing left,

[ocr errors]




and this result will equally hold whether a be 5, or 7, or 1000, or any other number whatever.

By the aid of algebra, therefore, we are enabled to analyze and determine the abstract properties of numbers, and we are also enabled to resolve many questions that by simple arithmetic would either be difficult or impossible.

A draughtsman or engineer has but little practical use for a too extended acquaintance with algebra, as nearly all the algebraic rules have been transferred to ordinary arithmetical computation, but as the algebraic system is so inwoven into the school and college course of instruction it is well for everyone to know something of the elements of the science.

Arithmeticians for very many years direction to a curve, that the wheel movhave made a study of the use of formula ing on the inside must assume a greater (this is Latin for the word form) in stat- angle at the axle than the outer wheel. ing problems and rules; these forms are It is evident from this that such varianearly all expressed in algebraic terms. tion of axial angles must be accomplished

The advantage to be derived from the by some device at the steering arms of use of these is that it puts into a short the stud axles. If these steering arms space what otherwise might necessitate be fixed at right angles to the axles so the use of a long hand verbal or written that the transverse drag link is of a explanation.

length about identical with the distance Another advantage is that the memory between the wheel bases, any effort to retains the form of the expression much turn the wheels in steering will shift the easier and longer than the longer method angles of both arms with the fixed axleof expression, and it may be remarked

tree equally, causing the axles to assume that those who once become accustomed

positions as radii from different centers, to the use of formulæ seldom abandon

which would cause sliding or rubbing. their employment.

To remedy this difficulty and secure the

proper angle of the axles the two steerSteering Axle of Automobiles

ing arms, y and ył, are inclined inward,

making the transverse drag link shorter Will you kindly explain, through the consulting column, the theory of the front axle

than the distance between the axle pivots. construction of automobiles?-C. 0. H.

If the drag link be forward of the axleIn turning a corner it is necessary, in · tree the steering arm will incline outorder to prevent side slipping of the wheel, with consequent wearing on the tires, that the plane of the wheel be tangent to the curve on which it is rolling.

Waterproof Canvas This curve is approximately the arc of a

Please print formula for waterproof canvas. circle, as may be seen from the accom

-). S. panying illustration. When turning, the four wheels of the vehicle should roll on

To make canvas waterproof, dissolve circles having the same center. If they one part of pure beeswax in two parts of do not, the wheel which does not roll gasoline, and paint the canvas quickly directly about the center will slip side- therewith. The gasoline will evaporate, ways, just in proportion to the amount and leave the wax in the fibers of the canthat it deviates from the circular arc. It vas. This must all be done in the open is obvious that when an automobile's air, and away from a flame or light or travel is changed from a straight-ahead 'fire of any kind.

: ward.

Lifting Magnets Will you be kind enough to give me a sketch and explanation of the lifting magnets used in machine shops ?T. H. W.

The accompanying sketches, Figures 1 and 2, represent two different forms of lifting magnets which are in common use at the present time. The views show a cross section. In Figure 1 two coils are wound about the ends of an iron bar, B, this bar being bent into the shape of a horse shoe. By sending a current through the coils AA, the iron becomes magnetized and will attract any magnetic substance such as iron or steel. Figure 2 shows a magnet of a different type. There is one coil, A, which is wound in a circular form. Both drawings will explain themselves.



Electric Limit Switches
What are electric limit switches ?D. J. M. -

It was found in operating electric elevators that more space was needed between the cab and the overhead sheaves at the upper end of the run, and that a deeper pit was also required at the bottom of the run, on account of the occasional slip of the brake. For, frequently, although the mechanical, automatic or limit stop on the machine would break the circuit and apply the brake near the end of the trip, there were cases

when the empty cage was required to ascend at full speed and the brake had become slightly worn and did not grip as firmly as usual—that the cage would go beyond the landing, and the additional space mentioned above was required to prevent a collision. This also happened sometimes at the lower end of the run when an extra heavy load was descending. A lack of care on the part of the operator in breaking the circuit in sufficient time, or the causes just mentioned, would cause the cage to run down to the bottom and bump. To avoid this, as an extra measure of safety, switches are sometimes placed at the extreme limit of the run, the line wire being carried up the hatchway through the switch and returned. These switches are opened by the car automatically if it should pass a certain point, and the opening of this switch breaks the circuit and at the same time supplies an extra strong emergency



[ocr errors]


[ocr errors]


Wheat Bin that Won't Leak Could you tell me how to build a non-leakable wheat bin?-H M. T.

The diagram herewith shown is an end view of the bin. The dimensions and structure can be seen at a glance. The hopper should first be built. Next put in the rafters, floor them, being sure to run the flooring crosswise and running out past where the studding will be. The studding should be cut on a bevel to fit the hopper.


To Color Electric Light Bulbs

emery cloth, B. Fold the edges over as Please print directions for coloring electric shown. The pencil point is placed in the light bulbs.-F. R. S.

crevice and moved up and down, resultBeat the white of one egg to a froth ing in a point as fine as may be desired. and mix with one pint of soft water. If the pencil is revolved between the Strain through a fine sieve, being very fingers while sharpening a round point careful that no bubbles remain on the will be the result. surface of the liquid. Clean and polish the bulb, and hang to dry. Half an hour later again dip the bulb and let dry. Now

Tests for Boiler Water dissolve ten to thirty grains of powdered dye, according to the degree of shading,

Will you please print some simple tests for

boiler water?-E. G. A. desired, in four ounces of collodion. Plunge the bulbs therein and dry as be- Test for hard or soft water: Disfore.

solve a small piece of good soap in alco

hol. Let a few drops of the solution fall To Produce Aluminum

into a glass of the water. If it turns Can aluminum be produced by any other

milky, it is hard water; if it turns clear, means than electrolysis ?-G. D. F.

it is soft water.

Test for earthy matters or alkali: Electrolysis is the only practical meth

Take litmus-paper dipped in vinegar, and, od known for manufacturing aluminum.

if on immersion the paper returns to its All attempts to make aluminum in the

true shade, the water does not contain electric furnace by reduction of alumi

earthy matter or alkali. If a few drops num with carbon have proved unsuccess

of syrup be added to a water containing ful. The product thus obtained is almost

any earthy matter, it will turn green. exclusively aluminum carbide.

Test for carbonic acid: Take equal

parts of water and clear lime water. If To Make Pencil Sharpener combined or free carbonic acid is presHow can I make a simple pencil point ent, a precipitate is seen, and if a few sharpener?-B. K.

drops of muriatic acid be added, efferveslin Take a paper dip, A, and a piece of A and a piece of ence commences.

Test of magnesia: Boil the water to twentieth part of its weight, and then drop a few grains of neutral carbonate of ammonia into a glass of it and a few drops of phosphate of soda. If magnesia is present, it will fall to the bottom..

Test for iron: Boil a little nut-gall and add to the water. If it turns gray or slate-black, iron is present. Second: Dis

solve a little prussiate of potash, and, if PENCIL SHARPENER IN USE,

iron is present, it will turn blue.


Marks. Cloth. 98 pp. 38 illustrations with index 1906. 5 in. by 74 in. New and enlarged edition. Tbe Technical Publishing Co. Ltd. London. Price 28. od.

[ocr errors]



392 pp.

55 Full page detailed


Of the many excellent treatises on

metallurgy and mechanical engineering Modern Plumbing Justrated. By R. M.

this little book varies from the beaten plates with index. 1907. 749 in. by 10% in. The path of dealing exhaustively with the exNorman W. Henley Publishing Co., New York. Price

traction and preparation of metals and

alloys, machines and structures, and In the author's preface it is stated that gives in handy form practical informathere is, perhaps, no branch of construc- tion to assist those using engineering mation work which has undergone within terials to make a selection. The short the same given time changes of a nature chapter on Metals for Bearings is alone so far-reaching as in plumbing construc- well worth the price of the book. tion.

As the work covers almost the entire Boiler Waters. By William Wallace Christie. field of plumbing, and is written in a Cloth. 235 pp: 71 illustrations with index. :206.

6 in. by 9 in. D. Van Nostrand Co., New York. Price clear and concise manner, illustrated with $3.00. detailed drawings it should be especially

Steam users in general will find the useful to the young men of the profes

information on water contained in this sion. The old-timers can also find much

book very helpful, especially in overcomto interest them in description of new

ing troubles arising from the use of methods of construction and use of cess

water. Next to the boiler itself, the pools, automatic control of hot-water

water to be used is the most important tanks, flushing, etc., and suggestions for

consideration in a steam plant. estimating.

The long chapters on corrosion and The practical hints so well illustrated

water-softening in addition to the chemwith the carefully made drawings are of

ical explanations give practical descripincalculable value to the up-to-date

tions and suggestions in a popular way plumber, as well as to owners of build

easily understood by the ordinary engiings who should know personally that no

neer. old-fashioned methods are used in their

So much trouble has been and is caused plumbing construction.

by boiler water, we think the author has

made no mistake in giving up this entire Modern Milling Machines. By Joseph 0.

volume to the subject. Of his many Horner. Cloth. 304 pp. 269 Illustrations with index. works we think this the best. and feel 1906. 6 in. by 9 in. The Norman W. Henley Publishing Co., of New York. Price $4.00.

sure it will be the cause of removing

much of the engineer's trouble, as well as The book is devoted entirely to the one

decrease operating expenses. department of machine shop practice, the milling machine, and the author handles

Brooke's Twentieth Century Machine the subject well, giving the history of its Shop Practice. By L. Elliot Brookes. Cloth. 661 development, and going into all the de pp. 423 illustrations with index. 1906. 5% in. by

7% in. Frederick J. Drake & Co., Publisher, Chicago. tails of the construction and operation of the earliest makes down to those of This book contains a large number of the present day.

useful rules, formulas and tables valuThe typical methods of holding work, able to Machinists, Engineers and others as well as some fixtures and jigs will interested in the use and operation of the serve as excellent guides to machine- Machinery and Machine Tools of a attendants and the chapter on feeds and modern machine shop. speeds will clear up many difficulties for Such subjects as Arithmetic, Mensurathem.

tion, Applied Mechanics, Measuring DeWe recommend this book, as about the vices, Shop Tools and Machine Tools, most comprehensive published, to every are treated in a very practical and nonpractical shopman who expects to keep technical manner. The chapter on Shop well posted on the latest phases of mill Kinks is a feature to be especially coming machine work.


« PreviousContinue »