No. 140. Toronto, Can., March 15, 1906.

I have some clean brass castings which I wish to dip bright. Will you kindly let me know the proportions of sulphuric acid and nitric acid to use for the dipping solution? Also, will it be necessary to pickle the castings first, and if so, what is the formula for the pick-ling solution? B. J.

The following is from "Polishing and Plating of Metals," by Herbert J.Hawkins: "A bright dip is one which is designed to obtain radically different results from the dull or satin finish dips. It is so composed that the metal, while corroded, is not covered with a dull sub-oxide, but remains bright enough to reflect the light more or less from the innumerable points left by the acid, so that while we have a matted surface, it leaves the metal bright and shining but not polished. Speed of operation and uniformity are the essentials in bright dipping, as the acids act very quickly, and the longer the work is allowed to remain in the dip, the more corroded and larger will be the granulations of the surface of the metal, and the duller will be the effect produced. Another very important point is the ability to keep water out of the dip without unduly slowing the outputof the work. Water will convert a bright dip into a satin finish dip, if present in a very small quantity, thus destroying the dip, as it will no longer give the best results as a bright dip. * * * Bright dips are used to obtain two or three distinct effects, which depend chiefly on the amount of time the acids are allowed to work upon the metal; a secand or two will give a bright effect, twice that length of time will give a very bright surface, while six or seven seconds will give a comparatively dull effect which is almost a satin finish. This time is given for a new dip which is working rapidly upcn metal very easily corroded, such as the brass generally used in gas fixtures. As the dip gets older the time must be increased to obtain similar effects, and metals less easily attacked must also have longer time.

" The bright dip for copper, brass, bronze or German silver is:

Sulphuric acid 100 parts by weight.

Nitric acid 75 " " "

Common salt 1 " " "

" After dipping, the articles should be very quickly rinsed in cold water, then in hot water and dried in sawdust. Boxwood or hardwood sawdust must be used; soft wood sawdust will not do, as it tarnishes the work badly.

" It may be stated generally that work to be dipped should be dry and free from grease. It is the usual practice with brass or bronze goods to first hot potash them, then swing in the air until dry, then immerse in the bright dip, then into clean running water, then in boiling water and finally dry in sawdust. In this way the potash dries quickly upon the surface of the work, forming a film which protects it from the air while being conveyed to the bright dip, * * * thus producing brighter and more even results in the finish.

Pickles are used to remove sand or grease from rough castings, preparatory to polishing or plating. A pickle for brass or copper that is not to be polished is: Nitric-acid 200 parts by weight.

Common salt 1 " " "

Lampblack 2 " " "

After pickling until clean, hot potash them, swing in the air until dry, then into the bright dip, etc., as above.

No. 141 Wolfboro, N. H., March 31, 1906.

I have two telephones made of just two bi-polar receivers, with a suitable call. 1 have tried it on a line about 150 feet long, of No. 12 galvanized wire, but I should like to hear a little better. 1 can talk over it now fairly well, but it is not near as loud as a commercial telephone. Could a battery be connected into the circuit with or without an induction coil, and give better results? If so, please send a diagram of the connections. Also, please send a diagram of the connections for a magneto call line of two stations about 1 1/2 mile apart. G. F. B.

The bi-polar receivers which you are using contain permanent magnets which, whenever the diaphragm vibrates as when spoken into, set up feeble alternating currents in the line and so influence each other. The addition of batteries to the circuit would cause currents to flow which would interfere with those set up by the magnets and serve to prevent the proper action of the receivers. Batteries can only be used in connection with the microphone transmitters. The diagram for the magneto circuit accompanies this answer.

No. 142. New London, Conn., April 9, 1906.

Will you kindly advise me how to take the solidly glued fingerboard from the neck of a violin? Also state how or by what process patterns, such as boat patterns, are made. Can you state where a varied line of cheap but reliable trade text books can be bought?

J. M. H

As the glue holding the finger board to the neck is old and absolutely dry, the first operation would be to use the edge of a thin-bladed knife as a wedge and get a crack started. Wet the crack with warm water, and after a few minutes use the knife again, continuing the process until eventually the glued surfaces will part.

The process for making boat patterns is quite fully described in the first chapter of the description of the tender contained in the March, 1906, number.

It will be necessary to know the subjects upon which books are desired before specific information can be given.