No. 85. So. NoRwalk, Conn., Jan. 23, '05.

Will you kindly answer the following questions relative to the battery described in the July, '03, number of Amateur Work :

1. The diameter of the tin cans ?

2. If cans were used 5 in. diameter and 10 in. high, what would be the correct dimensions for the wire gauze cylinder?

3. Can wire window screen netting be used in place of the 20-mesh gauze, as specified?

4. Can kerosene be used in place of the paraffine oil?

5. Should both the solution and oil be poured in the cylinder and on the filings?

6. What is the ampere hour capacity? F. B. H.

1. As mentioned in the description referred to, any tin can having lapped joints can be used; those with soldered joints will not answer, as the potash solution will attack the solder aud leaks will soon follow. Cans used for preserved tomatoes will answer and are easily obtainable.

2. The gauze cylinder could be made about 2 in. diameter and 9 in. high. The purpose of the gauze cylinder is simply to retain the filings in place and prevent them from coming in contact with the zinc.

3. If window screen netting is used any paint should first be burned off and the filings will have to be screened, and none used that pass through the screen. A larger quantity ot chips will be needed from which to get enough of the required size after screening.

4. Kerosene oil will not answer, and as paraffine oil is not expensive and is easily obtained of oil dealers, it should certainly be used.

5. The solution is poured into the cylinder before placing the zinc in position; it will fill any space around the filings and within the cylinder. The oil is then poured in and is used to prevent air from reaching the solution, potash having a great affinity for the moisture in the air as well as the oxygen.

6. Having had no personal experience with this cel1 would request any reader who has to give his experi ence in this matter.

No. 85 CLARKESVILLE, Ga., Jan. 17, '05,

Will you please tell me of the process by which I can make a cell of dry battery stronger after it has become too weak to use? S. C. K.

An exhausted dry battery may be partially revived by sending a current of low voltage through same in reverse direction from the discharge, or by punching a few holes through the pitch used to seal it at the top, and putting in a solution of sal-amoniac and water or salt in water. Ordinarily, however, it is more satisfactory to get a new cell. Another way is to punch holes in the sides and put cell into an ordinary glass preserve jar and fill up with the sal-amoniac solution, thus converting it into a wet battery.

No. 87. BaRRe, Vt., Jan. 11, '05.

What is the voltage of the Edison-Laland battery, type V. ? Can anyone cast the zinc himself ? E. N.

The E. M. F. of the Edison primary battery, type V., is .75 volt. It is made in two sizes, one giving 150 and the other 300 ampere hours. The zincs can easily be cast in wooden molds or in sand, but the oxide of copper cakes can only be made with suitable machinery, as a very heavy pressure is required to form them.

No. 88. Cleveland, Ohio, Jan. 12, '05.

Will you please give directions in your valuable magazine for making an induction coil which will give a good 12-in spark on a 20-volt current through the primary winding? E. A. H.

We quite frequently receive requests for descriptions for making large coils, but find that when the writer learns the cost of materials and the amount of work in_ volved in the making, the desire is satisfied with a coil of much smaller dimensions. As there is, however, a demand for a coil of fair size, to be used in X-ray experiments in connection with a high-frequency coil, we are having prepared a description of an induction coil to give an 8-in. spark, to be followed by a description of a high-frequency coil of a suitable size to work with it. The combination will be adequate to do excellent X-ray and other coil experimental work, and is recommended as being an excellent size for ambitious amateurs to attempt.

Dr. Haanel, Dominion Superintendent of Mines, who recently went to Europe to investigate methods of electrical treatment of ores, has received samples of grayr white and mottled pig iron, all having been reduced from the ore direct by the aid of an electrical furnace. Samples of castings made direct from the furnace are on exhibition, and are said to be of excellent quality. The gray pig is a superior quality of foundry iron, and can also be used for conversion into steel by the acid process.

An exhibit at the recent meeting of the Society of German Plumbers which attracted considerable attention was that showing an invention of Chemist Blau, of Augsburg, for the manufacture of fluid gas from the residuum of petroleum and heavy mineral oils. The inventor says this gas may be manufactured very cheaply where there is an abundance of petroleum, and that it may be transported from one place to another in cylinders as easily as carbonic acid gas. The gas may be used for lighting churches, halls and detached buildings, and small tanks may be used in lighting automobiles. The Blau gas makes a very brilliant light for street lighting, and is very difficult to explode.