No. 74. Chicago, ILL., Feb. 18,1904.

Being a reader of your paper, " Amateur Work" I would like to ask how a storage battery can be sealed up so as to prevent it from corroding at the connections. I have made and used quite a number and understand them fairly well, but cannot overcome this fault. v. A. S.

The creeping of salts from the electrolyte is a fault common to about all form of batteries. The best method of preventing this is to coat the exposed parts of the elements with melted paraffin. The other way is to adopt a form which will permit of sealing with pitch, but this is a difficult matter to do successfully.

No. 75. Chicago, III., Feb. 22,1904.

On Page 99, Amateur Work for Feb. 1904, it reads; -"Lay out a centre line, passing through the centres of the end edges and another at right angles thereto at the centres. Then lay off the three holes for the knife edges so that the upper edge of the holes at the ends just touch the line and the bottom edge of the centre hole does the same". There is a line on the beam in the drawing with the holes touching it but it seems to be about 1-32 inches above the centre of the beam, the 1-16 inches shown appearing to be at the centre. Where are the holes located with reference to the horizontal centre of the beam? Would a line touching the edges of all the knives be in the centre " up and down" of the beam? H. H. B.

The upper side of the holes for the end knife edges, and the lower edge of the hole for the middle knife edge lie on one straight line which is 1-32 inch above the centre line of the beam. In all balances the knife edges must lie in the same plane.

No. 76. Anderson, Ind. Feb. 22,1904.

Please send me instructions for finding the amount and size of wire to be used on dynamo the size and shape of the accompan-ing cut not shown, to produce 110 volts and 4 amperes; f it can be wound for that. If not, the highest E. M. F. possible. J. W. J.

This dynamo cannot be wound for four amperes at 110 volts. It might give two amperes at that pressure, or four amperes at 55 volts. There are not enough slots, even with two coils in each slot, for so high a voltage. For 110 volts there should be at least 20 slots. If that number is used they would be 5-16 inch diameter. Armature should be wound with 20 coils of No. 24 double cotton covered wire, 16 turns per coil, two coils or parts of two coils in each slot. This would require about 300 feet of wire. The field magnet core should be at least 2 inches in diameter instead of 1 3-8 inches. This could be wound with 25 layers of No. 30 single or double coiton covered wire. This would require about 3000 feet. The pole pieces come too close to each other; 1 inch or 11-4 inch would be much better than 1-2 inch as shown in the drawing. Speed, 2000 R. P. M.

No. 77. Charlestown, Mass. Feb. 20,1904.

I have a few questions to ask and would be greatly obliged if you will answer them. A. About what would be the cost of two ebonite disks, about 19 inches in diameter and 1-8 inch thick. Where is a good place to buy ebonite? B. Would it be convenient for you to give directions for making a 1-4 H. P. air engine in one of your future numbers? What would be the cost of materials? What is the cost of running a hot air engine as compared with a steam engine? C. What does aluminum cost per pound and where may it be bought? R. C. H.

Two discs of hard black fibre would weigh about three pounds and cost about 50 cents per pound. I think you can obtain them from Chandler & Farquhar Co., 34 Federal St. Boston, Mass.

A hot air engine of about 1-8 H. P. is in this issue. From it you can get a general idea of size and shape for a large one. The author is arranging to supply castings which can be finished to any desired extent, the price of which has not yet been determined. The cost of sheet aluminum depends upon the gauge-It can be purchased of A. J. Wilkinson & Co. 180 Washington St.