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thus secured enables the diver to lift the fuel tank forms no part of the strucobjects heavier than he could otherwise ture of the hull itself, and in case there handle. In addition to this improvement is any damage to the hull, the gasoline over the old method, a high-power elec- will not find its way into the interior of tric light that will penetrate the water the vessel, and in this manner be a source for some distance is placed in the helmet. of danger, but the fuel will pass outside,

and all risk is thus avoided.

Latest Torpedo Boat

To Stop Runaway Car A GASOLINE torpedo boat is the

latest addition to the British navy; THE New Jersey and Hudson River The 60 in

, nine feet in beam, being much smaller an unusual kind of stopping device for than the average steam-propelled torpedo the steep places on the Palisades, along boat. The vessel has these advantages: the Hudson. The cars ascend the cliffs It is small, light and fast. It will carry in a zigzag course at an average grade a load of three tons, is equipped with of 7 per cent. In the event of a car's three propellers, and can make twenty- running away, a siding track, with the four knots an hour.

switch point always in direct connection It is maintained by eminent naval en- with the main track, serves to draw off gineers, that on account of the small size,

the car. The rails of this siding are the shallow draft and great radius of always buried in sand. The friction action, as well as the very great speed between the sand and the wheels, of shown by this form of torpedo boat, course, brings the runaway at once to a success is assured for this type of craft stop. On each side of the switch rail is for coast defense purposes, and it is built a trough, which holds the sand. clained that it also has given excellent The rail is covered to a depth of two and account of itself in rough seas, with very

one-half inches. Numerous tests have little wash when traveling at full speed. proved the efficiency of the apparatus.

One of the important and interesting The device should be of value in savpoints in connection with this boat is that ing property and lives.

Persian Carpets

By H. R. Thompson

T frequently happens, in of the performance of his tasks, and consequence of industrial where the monotonous discipline of the development and the tech- workshop may not be imposed. From nical skill resulting there- time to time, even the most industrious from, that a traditional in- worker will stop to smoke his. water-pipe,

dustry disappears from drink his tea, and enjoy a siesta. It may the land of its birth, killed by outside be added that the climate is such that the competition. So, Venice—for example— continuous, uninterrupted toil of western has long since ceased to be the center for workshops does not seem to be possible. the manufacture of mirrors; but it Hence the industry has been modified seems now, on the other hand, as only within the limits of local customs. though Persia would still continue to be This statement is based principally upon the producer of carpets. In short, “Per- the results at Sultan-Abad, where the sian carpet” is not a mere name. The two undertakings have been established proof is that the customs reports of the along lines that will be appreciated in Empire of the Shah, imperfect and in- Europe. One of these houses belongs complete as they are, show an annual ex- to a Manchester firm; and in spite of the portation of from 3,000 to 4,000 bales of opposition of the native merchants and carpets, valued at not less than $350,000. courtiers, who feared the competition,

Carpet-making may be considered to they have succeeded in enlisting the servbe the true natural industry of Persia; ices of a goodly portion of the populaand, being carried on in the most primi- tion of Sultan-Abad and the surrounding tive fashion, it occupies thousands of villages. At present there are about hands. It is not only the fixed popula- 5,000 workers, producing an annual outtion that engage in it, but the nomads put valued at about $1,000,000. The also. The whole world knows of the European house has offices at the gates carpets of Shiraz, of Kirman, of Meshed, of the city for its own employees, as well of Sultan-Abad and Tauris. A curious as warehouses for the storing of goods, fact is that the industry has just received and a dyeing establishment where the a new impulse, by which it will be en- wool is prepared for the use of families abled to meet European competition, for working at home; for no worker is pernew blood has been infused in the form mitted to provide his own wools, since the of foreign capital, which has established chances are that they would be colored large houses, without disturbing the na- with anilines and thus be iable to a. tives in the most important of their na- rapid change of shade. We have said tional habits. There are a number of that the work is that of the family. centers devoted to the manufacture of Practically the man, the head of the carpets, of a class and variety fixed by family, acts as a contractor and agent what is found in the district or the tribe, with the European house, while his nuwhose models and methods are identical. merous wives first, and then his young But everywhere, even in the region of daughters, work at the fabric by hand, Tauris and Sultan-Abad, where, as we which frequently requires the continuous have said, the European promoters and labor of three months for a single piece. dealers have been most active, the native The European house not only furprefers to work at home, in order that nishes the wools; but every time an orhe may be at perfect liberty in the matter der is placed, it gives the contractor a

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specification of the weight, and a draw- price, according as the work may be ing showing the dimensions and design found to be satisfactory or to leave someof the carpet to be made. All of these thing to be desired. specifications, as they might be called, are Finally, it may be added that at Tauris issued in duplicate, so that, when the car- there are about 2,000 persons employed pet is delivered, the payment is made in a similar way making carpets for exwith a premium or a reduction in the port.

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Are you worried by any question in Engineering or the Mechanic Arts? Put the question into writing and mail it to the Consulting Department, TECHNICAL WORLD MAGAZINE. We have made arrangements to have all suck questions answered by a staff of consulting engineers and other experts whose services have been specially enlisted for that purpose. If the question asked is of general interest, the answer will be published in the magazine. If of only personal interest, the answer will be sent by mail, provided a stamped and addressed envelope is enclosed with the question. Requests for information as to where desired articles can be purchased, will also be cheerfully answered.

Making a Pipe Rack

16/2 inches and a width of 512. The I am constantly losing my smoking pipes.

dimensions of the lower shelf and the I should be very glad to have you give a brief

brackets are indicated in the drawing. description of how to make some sort of a rack The rack may be made of oak, pine, to keep them in.-0. W. W.

maple or mahogany, as desired. Your question will be best answered by the accompanying drawing, the various parts being shown in section and to

The Lalande Cell gether. The upper shelf may be built What chemical action takes place in the Lawide enough to hold the tobacco jar, lande cell?—R. O. match safe, etc. The dimensions of the The elements of this cell are two amalrack are, for the upper shelf, a length of gamated sheets of zinc, between which is

the inactive plate, consisting of a compacted

mass of black oxide of joog

E-N

copper, all suspended in a solution of caustic soda

caustic potash of about 1.16 specific gravity. The electromotive

force of this cell is at 9023

first as high as 1.2 volts, due to the free oxygen in the copper oxide, but when this is exhausted the voltage falls to 0.82,

at which it remains unHOME-MADE PIPE Rack.

til all the copper oxide

or

is reduced to metallic copper. Then a the worm, B, which is surrounded by cold further drop in voltage occurs.

water, and finally issues at H as disWhen this point is reached the cell tilled. A baffle plate, F, may be located should be regenerated by removing the in the head of the still to prevent any copper plate, washing it with clear water, water from being carried over mechanand exposing it to the action of the air ically in case the water in A should boil at a temperature of 220° to 250° F. for too violently. an hour. The copper is thus oxidized to In works where only a limited amount

of pure water is required, it is sometimes the practice to condense direct steam from the boilers, or indirect steam that has already been used for heating

purposes or otherwise. In this way a

GOUTLET comparatively pure water is obtained, but STEAM

its purity cannot always be depended INLETA

upon, as oil, which is volatile with steam, is likely to get into it in various ways, and iron rust from steam pipes occasionally causes trouble.

WATER

STEAM
OUTLET

COLD
WATER

DRAW
OFF

WATER DISTILLER.

Electric Transformer copper oxide, and can be used with its

1: On an alternating current dynamo can original efficiency. The liquid also should a transformer be used to change the high elecbe replaced when it shows precipitate of

tro-motive force to a high amperage ? zinc hydroxide.

2: Can a motor or dynamo be wound with

same size wire on the field magnets as that The chemical actions are as follows:

upon the armature, and would you get prac(1) Zn + 2NaOH Zn(OH)2 +

tical results from this treatment? Na.

3: Please explain what transformers are

used for.-H. A. (2) Na, + 2H,0= 2NaOH + Hz. (3) CuO + H, = Cu + H.O.

1: A transformer can be used to (4) Zn(OH)2 + Na(OH)2 Na,

change the high electromotive force of ZnO2 + 2H,O.

an alternating current generator to low The liquid becomes a solution of

electromotive force, the current at the sodium zincate which permits zinc hy

same time being changed from small to droxide to settle out as a precipitate.

large in the same ratio. This is one of the great advantages of alternating current, that its electromotive force can be

stepped up or down at will by the transTo Distill Water

former, which is cheap, very simple in Will you please describe a small still for

operation, and very efficient. making distilled water?-H. L. B.

The still is shown in the figure. A still of this kind may be heated by direct gas flame or, what is better, by a steam coil inserted within the still, or by a

A А steam jacket. The figure represents a cross section of such a still. The water in the still, A, is constantly kept at the level of the water in the condenser, B,

Electric TRANSFORMER. by means of the cross connection, C. Steam is introduced into the jacket, J, The arrangement for doing this is through the valve, D, and escapes through shown in the accompanying sketch, valve E, and by properly regulating these where A represents the alternator, P valves, the water in A may be boiled represents the primary of the transformsteadily for hours.

The vapor passes er, S represents the secondary, and LL over through the neck, G, condenses in

represents the line. In case we wish

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