Part 8

(12) F. C. A. writes: I wish to construct a bar electro-magnet to go in a cylinder 1 inch in diameter and 1 inch long. 1. What size ought the core to be? What number of wire shall I use, and what number of Léclanché cells shall I use (not to exceed twelve) to obtain the greatest possible attractive power, distance 1/10 of an inch? A. Make the core 3/8 inch, wind it with No. 24 silk covered wire. Use 6 or 8 cells. 2. In the same space, could a horseshoe magnet be used, with a gain of power over the bar magnet? A. A cylindrical magnet, which is substantially the same as a horseshoe, might be substituted with advantage for the bar magnet.

(13) W. C. H. writes: In turning a tapering shaft in an engine lathe, will the tool if raised above the centers of the lathe turn the taper true from end to end, _i. e._, neither concave nor convex, the taper to be made by sliding the tail center the required distance? A. The taper will be concave.

(14) H. E. H. asks how to make lime light. A. The lime light is made by directing the jet of an oxyhydrogen blowpipe against a cylinder of lime. The blowpipe is contrived to take the proper proportion of oxygen and hydrogen gas, and the lime is placed in the reducing focus of the jet.

(15) L. F. asks: 1. How many Daniell's or Smee's cells would it require to produce the same effect as 50 Bunsen cells? A. About 100. 2. Is the diaphragm equally necessary in Bunsen's, Smee's and Daniell's cells, or can it be omitted in any one of them easier than in the others, and why so? A. The diaphragm or porous cell is required in Daniell's and Bunsen's batteries, but is not used in Smee's. The porous cell is used only in two fluid batteries; its object is to allow the current to pass, but to prevent the mixture of the two liquids. 3. Is the thickness of the zinc of any importance? A. Only that the thicker zinc lasts longer. 4. Which is the cheapest way to produce electric sparks and to charge a Leyden jar, and what will be the expense? A. By means of a frictional electrical machine. The machines cost from $10 upward.

(16) R. C. K. writes: I am an engineer by trade; have been at it 9 years. Am out of a position at present and want to learn mechanical draughting. How long would it take me to become a good draughtsman by taking a special course at some university? And with my knowledge of engineering and draughting, would my services be likely to be in fair demand? A. If you are familiar with mechanical operations, you might become a good draughtsman by close application under a competent instructor for one or two years. At present there are many excellent draughtsmen looking for positions.

(17) G. B. M. asks for the cause of the ribs or ridges on the surface of a piece of timber which has passed through a planing machine. A. They are frequently due to the intermittent motion of the feed.

(18) A. F. writes: Having a small quantity of gold and gold plated things, I would like to know the simplest way to melt it. A. Put it in a small crucible with a little borax and melt in a common kitchen fire.

(19) J. H. S. writes: I have three drawings each 21 x 30 inches, which I wish to mount upon cloth like a map, placing them end to end so as to make one whole sheet 90 inches long. The drawings are upon heavy Whatman paper. A. You should stretch wet canvas or factory cloth upon a frame, and while it is still damp apply paste to the backs of the drawings and lay them smoothly on the stretched cloth. When the paste becomes thoroughly dry cut the cloth from the stretching frame and paste a tape binding around the edges.

(20) P. M. asks: What is the difference between the inner and outer rails of a 10° curve 100 yards in length, gauge 4 feet 8 inches? A. If this 100 yards is measured on the center of the curve, whose radius in R - 2-1/3 feet is R, the length of the inner rail is --------- X 100, and of the R R + 2-1/3 outer tail --------- X 100. R

(21) W. B. K. asks how to make a shoe dressing for ladies' shoes. A. Soft water, 1 gallon; extract of logwood, 6 ozs.; dissolve at a temperature of about 120° Fah. Soft water, 1 gallon; borax, 6 ozs.; shellac, 1½ oz.; boil until dissolved. Potassium dichromate, 3/8 oz.; hot water, ½ pint; dissolve, and add all together. It is preferred to add 3 ozs. of strong aqua ammonia to the liquid before bottling.

(22) J. D. asks: What chemicals can be put into water to increase its efficiency in extinguishing fire? A. Carbonic acid; sodium carbonate.

(23) H. P. writes: Please give me the advantages and disadvantages of substituting a galvanized iron tube 18 inches in diameter and 20 feet high for a wood tank, 5 feet wide and 6 deep, as a container of water in a dwelling house in the country. Would the narrower body of water keep fresh or sweet longer, etc.? Also the thickness of iron necessary to safety, and the number of gallons of water this tube would hold. A. The advantages are in favor of the wooden tank; zinc lined vessels (galvanized) are unsuitable for reservoirs for potable water. See p. 369, vol. 36, SCIENTIFIC AMERICAN. 0.3 inch iron would be stout enough. A pipe of the dimensions specified would contain about 327 gallons when full.

(24) F. L. M. asks: 1. What is the process by which wire is given a copper finish? A. Clean the wire by pickling it for a short time in very dilute sulphuric acid and scouring with sand if necessary. Then pass the clean wire through a strong bath of copper sulphate dissolved in water. 2. Can wire be thus finished and also annealed? If so, how? A. The wire should be annealed first. 3. What other finish can be put on iron wire (annealed), and by what process? A. Zinc--by passing the clean wire through molten zinc covered with sal ammoniac; tin--by drawing the wire through a bath of molten tin covered with tallow.

MINERALS, ETC.--Specimens have been received from the following correspondents, and examined, with the results stated:

J. H. McF.--A fine quality of kaolin.--F. C. H.--The floury powder consists chiefly, if not altogether, of calcium carbonate.--C. L. G.--They are all silicious limestones. We cannot judge fairly of their value for building purposes from the powders sent.--D. K.--Ferruginous earth or marl.--A. E.--It is a partially decomposed feldspar. The white powder is for the most part an impure, silicious, kaolin.--E. H.--It consists chiefly of basic carbonate and hydrated oxide of lead--poisonous.--J. B. V.--It is a fair quality of pipe clay--impure silicate of alumina--probably worth about $2 per ton in New York.

* * * * *

=COMMUNICATIONS RECEIVED.=

The Editor of the SCIENTIFIC AMERICAN acknowledges with much pleasure the receipt of original papers and contributions on the following subjects:

Religion. By W. M. E. Cause of Explosion in Flouring Mills. By G. M.

* * * * *

[OFFICIAL.]

INDEX OF INVENTIONS

FOR WHICH

=Letters Patent of the United States were Granted in the Week Ending=

=May 28, 1878,=

=AND EACH BEARING THAT DATE.=

[Those marked (r) are reissued patents.]

A complete copy of any patent in the annexed list, including both the specifications and drawings, will be furnished from this office for one dollar. In ordering, please state the number and date of the patent desired and remit to Munn & Co., 37 Park Row, New York city.