No. 143. Meriden, Conn. May 3, 1905.

Will you kindly advise me whether it would be feasible to light my residence with a small lighting plant operated by myself. I have but little acquaintance with electrical matters and would not feel like investing any considerable sum in an outfit which required constant attendance by a skilled electrician. Would it be of any advantage if several of my neighbors combined with me and a larger plant was purchased ? My residence is located some miles from the center of the city and the lighting company does not seem disposed to extend the wires the distance required to supply the section where I am living. H. S. C.

Isolated or self-contained lighting plants are now becoming quite common throughout the country, and if the first cost is not objectionable, a private lighting plant is both satisfactory and inexpensive to operate. The cost of lighting could undoubtedly be made much less than the rates required by the regular lighting company. You do not state the number of lights required, so exact cost of outfit cannot be given. Assuming that the residence contains ten rooms and that twenty lights would be the maximum load, the required output from the dynamo would be about 1000 watts, and a 2-k. w. dynamo would be desirable, running tte same with a 3-h. p. gasoline engine. The cost of engine, dynamo, switchboard and switchboard instruments would be approximately $350 or $400.

Owing to the fact that the lamps can be lighted only when the dynamo is in operation, it would also be desirable to have a storage battery, and to keep the number of cells of the battery as small as possible a 55-volt current should be used. Thirty cells in the battery would then be sufficient, which would give two spare cells for use when the battery was nearly run down. Lamps of standard size can be obtained at about the same cost as for the usual lighting circuit voltage, 110 volts.

With a storage battery the size of the dynamo could be reduced to 1 k. w. and a smaller engine used, and the " peak of the load " between five and eight P. M. could be taken care of by the battery. With such an outfit the dynamo could be operated at any convenient time during the day or evening for charging the battery, and the lighting current drawn direct from battery. This would permit of the lamps being lighted at any time of the night, whether the dynamo was in operation or not. When the full number of lamps are required to be lighted, the current could be taken from both dynamo and battery.

Undoubtedly some young man could be found in your vicinity sufficiently acquainted with the operation of a simple outfit of this kind who would operate it for a limited time until you acquire sufficient experience to dispense with his services. Such lighting plants are very desirable and economical for any one willing to devote a small portion of their time to looking after its maintainance and operation. The expense of operation would be very small, costing not more than two or three cents per thousand watts as against 15 or 18 cents charged by the regular lighting companies.

No. 144. Seattle, Wash., May 6, 1906.

I recently saw a small model ship enclosed in a glass bottle and would like to know by what process the ship was constructed and placed in the bottle. The ship was considerably larger than the mouth of the bottle, and the bottle did not show any break so that, apparently, the model must have been made in pieces and put together inside of the bottle, which would have been a very difficult operation. Was it not done in some other way, and how? H. T. W.

Models contained in bottles are frequently constructed in the way you state. They are also made up outside of the bottle; the bottom of the bottle is broken off in a special way and then remelted on so skilfully that no trace of the joint appears. Another way is to have bottles made with the neck unshaped, and after the model is placed inside the necks are drawn down to the usual small size.

No. 145. Chicago, III., May, 1906.

Some years ago the newspapers of this city men. tioned an invention of an explosive which could be fired from high powered guns, and which was unex-plosive until it came in contact with water, when it exploded with great violence. Since then I have heard nothing more of the matter, but am interested to know what substances explode upon coming in contact with water. J. W- C.

Two substances which will explode or give a semblance of explosion upon contact with water; these are the alkali metals, potassium and sodium. If a small piece of either metal is brought into contact with a small portion of water the water decomposes the metal evolving hydrogen and the heat of the reaction is so great that the gas takes fire with a slight explosion.

If potassium be thrown into water, the hydrogen given off will take fire, but this is not true of sodium which has a less powerful reaction and does not produce a sufficiently high temperature to ignite gas when brought in contact with a large quantity of water. In handling both metals great care must be used, as the moisture of the fingers will frequently cause them to unite. They must also be kept in air-tight receptacles, as they oxidize rapidly when exposed to moist air. Presumably the explosive you mention as being reported in the papers was some high explosive which was exploded by means of one of the two metals here mentioned, as neither of these two metals would have caused an explosion of sufficient violence to be valuable for commercial purposes in warfare.

No. 146. Newark, N. J., May 8, 1906.

Will you kindly advise if it is possible to solder a leak in a lead pipe in through which water is flowing.

A. L. R

It is not possible to solder lead pipes containing water, as the heat of the solder is drawn off so rapidly that it will chill on coming in contact with the pipe. We presume that for some reason it is not desirable to shut off the water, in which case the only way in which the pipe can be soldered is as follows: - Cut off the pipe at the leak with a hack saw and fill the feed end with a "stop back" made of very soft well kneaded clay or piece of soft bread or dough. This stopback should be forced 6 or 8 in. from the end of pipe. The pipe can then be soldered as usual, using a flux. Care must be taken not to have the stop back so hard as to prevent the water from eventually soaking through it and forcing a passage.

If it is possible to run a stout string through the empty section of the pipe, the end of the string could be carried through the stop back. After the joint is soldered, pull out the string, leave a small hole and the water will pass through it and eventually clear out the pipe.

No. 147. Philadelphia, Pa., May. 4, 1906.

I am using a magneto to spark a small gas engine. The spark is quite feeble and the magneto does not seem to be giving a very strong current. Will you please inform me what may be the matter with it?

G. E. M

Magneto igniters are constructed with permanent magnets. The magnetism in such magnets becomes weak in time and they require to be remagnetized. If you are acquainted with any one in an electric lighting station you could probably take the magnets to the station and have them remagnetized. There are also electrical manufacturing concerns in your city who could do it for you at small expense. It would be well to thoroughly examine the spark plugs and all connections to ascertain if the fault really is with the igniter, as it frequently happens that a poor connection or spark plug will cause trouble which may seem to be with some other part of the sparking apparatus.

To find the diameter of a driven pulley, when diameter and speed of driver and speed required are known, multiply the diameter of the driver by its speed of revolution, divide by the required speed; result will be the diameter of the driven pulley. To find the speed of a driven shaft when the speed of driver, diameter of driver, and diameter of driven pulley are known, multiply the »-peed of the driver by its diameter and divide by the diameter of the driven pulley; the result will be the speed of the driven pulley. To find the diameter of driver when the diameter of the driven are known, multiply the speed of the driven pulley by its diameter and divide by the speed of the driver; the result will be the diameter.