The Thomas A. Edison Papers Digital Edition

Transcription

March 26th., 1896. 
Edison United Phonograph Company, 
G. N. Morison, Esq., Secretary, 
Mills Building, Broad St., N. Y., 
Gentlemen:- 
Answering your letter of Feb. 24th., I attach herewith the formula for making up wax for use in connection with my Phonographs. This also gives information relative to the plant necessary in connection with same. Please acknowledge receipt. 
Yours very truly, 
Thomas A. Edison March 26th., 1896.
FORMULA AND PLANT REQUIRED FOR MAKING PHONOGRAPH WAX.
600 pounds of the best grade of stearic acid is melted in a lead lined iron kettle and filtered through soft, closely woven canvas, (such as is used in filtering pumps) into another kettle of copper, heavily plated on the inside with silver. The silver lined kettle should be heated by coal or gas, and so arranged that the upper half of the kettle is not exposed to the direct heat of the fire. Proper dampers for regulating the temperature should be attached. After the stearic acid has all been filtered into the silver lined kettle, the temperature is raised to 260 deg. Fahrenheit. Little by little 174-1/2 pounds of crystalized carbonate of soda is added, allowing the temperature to reach 320 deg. Farenheit, after about two-thirds of the carbonate of soda has been added. Care must be exercised in this operation or the wax may foam over. The carbonate of soda is best added by means of a one gallon silvered copper dipper, having a handle of iron five feet long. This is filled with the crystals of carbonate and submerged into the molten mass of stearic acid, and constantly stirred around until all the soda has been dissolved, when it is again filled and  the operation repeated until all the soda had been added. If during the operation the mixture boils so furiously as to be in danger of boiling over, the dipper can be removed, thus stopping further violent boiling. When all the soda has been added, the temperature is then raised to 430 deg. Fahrenheit and 102-1/2 pounds of stearate of Alumina is added and well stirred, then 125 pounds of white ceresine, and the mass is then kept at 430 deg. Fahrenheit to 440 deg. Fahrenheit, until bubbles and foam cease to form and rise to the surface.
Foaming off to the proper point is of great importance, for if not properly foamed off small pin holes will develop in the cylinders. The foaming off usually requires about one hour. The operator, however, should judge by the appearance.
The temperature is now allowed to fall to about 380 deg. Fahrenheit, when it is strained through three or four thicknesses of finely woven muslin and poured into pans to cool, if not to be used at once.
If it is wax desired to mould the cylinders from the same kettle in which the wax is made, allow the temperature to fall to 340 deg. Fahrenheit and then stand for some time so as to settle what dirt has gotten in whilst making.
The best wax should have a congealing point of about 260 deg. Fahrenheit. The method of observing the congealing point is as follows: Remove a ladle full from the main body of the wax when finished, and place a thermometer therein, then watch for the point at which a skin begins to form on the surface. If the congealing point falls below 260 deg. Fahrenheit it indicates a deficiency of soda in proportion to the stearic acid. If the congealing point is above 260 deg. Fahrenheit then soda exceeds the necessary amount and more stearic acid should be added. These differences will frequently occur with different lots of carbonate of soda, due to varying amounts of water of crystalization in the compound. Selection of Materials.
Great care should be exercised in purchasing the ingredients used in making the wax, if a uniform product is to be maintained.
Stearic Acid.
This should be the finest quality that can be supplied. It should be especially free from celic and subassic [sebacic] acids, or they form combinations with soda which takes up moisture from the air, which causes the surface of a cylinder to change, thus greatly impairing the quality of a record in a short time.
Carbonate of Soda.
This should be free from potash and silica, and should have the formula Na2 CO3 10(H20).
The carbonate of soda crystals should be picked over and only the well formed crystals taken. These are washed with a small amount of water and allowed to drain until dry, but must not be left exposed to the air very long before use. The imperfect and dirty crystals are dissolved in water, strained through a filtering cloth and crystalized.
Stearate of Alumina.
The plant for making this material consists of a steam jacketed kettle of about forty gallons capacity, three large wooden (cedar) tanks, each of about 1000 gallons capacity, a screw press, such as is used in rendering fat, a steam heated drying oven, containing trays made of canvas, stretched upon wooden frames, the total area of which should be about fifty square yards.
Operation——Caustic soda, as pure as can be obtained commercially, is dissolved in water and brought to 1,200 specific gravity, at 60 deg. Fahrenheit, and left to settle for several days. For this purpose three twenty-five gallon stoneware jars are provided, and 200 pounds of stearic acid is melted in the jacketed kettle and 65,232 Cubic Centimetres of caustic soda solution are added, with constant mixing. The mixing should be continued for some time, after all the alkali has been added. The contents of the kettle are then transferred to one of the large cedar tanks about three-fifths full of clean water and dissolved, the water being heated to boiling point by direct injection of steam. After all has been dissolved, the solution is run off through a strainer into another large cedar tank. A solution of common alum is now run into the hot solution with constant stirring. This will cause the stearic acid held in [illegible] solution to precipitate as Stearate of Alumina. The addition of the alum is continued, though slowly towards the last until blue litmus paper turns red when emersed [immersed] in the same. Care should be exercised so as not to exceed beyond the point where the paper first turns red, or a waste of alum will result. The watery solution is drained from the precipitate, and the latter is well washed with fresh water and finally drained on muslin stretched on a wooden frame, and then pressed to remove most of the water, after which operation it is spread in thin layers on the canvas trays, placed in the oven and dried for at least three days at 170 deg. Fahrenheit.
The stearate of Alumina should be perfectly dry before using. When a stock is made up ahead it should be kept in tightly closed boxes.