368 On the Method of printing upon Stone, [May, 



coinage of this country, I do not find any mention made of the 

 presence of gold. The old silver coinage had a certain propor- 

 tion of pure gold; and every ounce weight of the present new 

 coinage contains about \ of a grain of pure gold ; this I have 

 lately ascertained by a regular analysis. 1 send you enclosed the 

 exact quantity of pure gold, which is contained in every shilling 

 of the new coinage. 



Article XII. 



Observations on the Method of printing upon Stone, and on the 

 Composition of the Ink.* 



Any calcareous stone, which is compact, with a fine and equal 

 grain, susceptible of being polished with pumice, and capable of 

 absorbing a little moisture, may be employed for lithography. 

 It was supposed, for some time, that the stones used at Munich 

 alone possessed the necessary properties ; but suitable materials 

 have now been found in many of the departments of France. 

 Among others, there are strata of calcareous stone in the moun- 

 tains which separate Rufiec from Angouleme, which are well 

 adapted for this kind of work. 



In order to compose the ink, a vessel varnished and luted on 

 the outside is warmed ; when it is warm, we introduce one part 

 by weight of white Marseilles soap, and the same quantity of 

 pure mastic. These substances are melted and carefully mixed 

 together ; five parts by weight of shell lac is then incorporated 

 with them, by stirring them together until the whole is completely 

 united, and there is then gradually added a solution of one part 

 of caustic soda in five or six parts its bulk of water. This addi- 

 tion must be made cautiously ; for if the alkaline ley be poured 

 in all at once, the liquor would froth up, and rise above the sides 

 of the vessel. 



When these substances are completely mixed together, by 

 employing a moderate heat and the agitation of a spatula, the 

 necessary quantity of lamp black is added, and immediately after 

 as much water as is sufficient to render the ink fluid and in a 

 proper state for writing. The ink is applied to the stone as it 

 would be to paper, either by a pen, or a pencil. When the 

 design or writing is dry, and we wish to print from it, water, 

 acidulated with nitric acid, is employed, in the proportion of 

 50 parts of water to one of acid ; by means of a sponge the 

 surface of the stone is soaked with this water, taking care not to 

 rub the ink lines ; this process is repeated as soon as the stone 



* Translated from (he Journ.de pharm. March, 1817. 



