384 transactions of the american institute. 



An Improvement in Making Electrotype Plates. 



Mr. Silas P. Knight. — It is well known that when wa.x; or gutta percha 

 molds, coated with plumbago, are placed in or connected with a battery, 

 and a deposit of copper or other metal made upon the surface of the mold, 

 the action is at first slow and confined to particular parts of the surface; in 

 some cases several hours being requisite to produce a uniform and unbroken 

 metallic covering throughout its whole extent. The process invented by 

 me will cause the deposit to be uniformly diffused over the whole surface 

 of the mold at the instant of its immersion in the battery solution, thus 

 saving several hours' time and insuring a deposit of uniform thickness. 



The mold or matrix is made in the usual manner, and coated with plum- 

 bago; it is then placed upon a table, with the face upward; a saturated 

 solution of blue vitriol or sulphate of copper is sprinkled upon it, moisten- 

 ing the entire surface; lapon this I scatter from a fine sieve cast iron filings, 

 the finest dust being most suitable for this purpose. The dust being sifted 

 upon the mold, is then distributed as uniformly as possible over its surface 

 by means of a flat camel's hair brush, which is passed rapidly and with a 

 light touch over the coating of plumbago. During this process, the solu- 

 tion of sulphate of copper is decomposed, and metallic copper is deposited 

 in a thin film over the whole surface of the mold. This brushing or dis- 

 tribution of the fine particles of iron does not require more than five 

 minutes for an area of five feet; at the end of which time the mold is 

 found to be coated with a thin film of copper over its whole surface as 

 above stated. The mold is now cleansed by allowing water to flow over 

 it, thus removing the solution and the remains of the iron dust; it may then 

 be placed in the battery and the connection made, when it will be found 

 that the deposit commences on all parts of the surface at the same instant, 

 thus insuring a uniform thickness of the metal, and diminishing to a great 

 extent the time required for exposure of the mold to the action of the 

 battery. 



All Harper & Brothers' plates for their weekly newspaper, monthly maga- 

 zine, &c., &c., are electrotyped by this process. 



I have received letters patent for the above process. 



The Chairman. — This formula indicates the changes, Cu. S. 0.4-{-Fe.= 

 Cu.-|-Fe. S. O4. The sulphuric acid leaves the copper and combines with 

 the iron. 



Mr. Goodman. — You ought to put one of the O's with the copper and 

 with the iron. 



The Chairman. — Yes, I know, by the old theory. But this is the empiri- 

 cal formula, and it is a great deal simpler than the rational formula. You 

 see that the elements are all the same. 



New Lactometer. 



Prof. Seely. — I hold in my hand a lactometer which I have designed and 

 tested. The nourishing parts of milk are the butter and the cheese or 

 casein ; and as the proportion of these two to each other is pretty constant, 

 if we measure the quantity of butter, we ascertain the value of the milk. 

 As the petroleum oils dissolve all fats, I have designed this instrument for 



