608 PHILOSOPHICAL TRANSACTIONS. [aNNO 1780. 



//. Of some New Experiments in Electricity, with the Description and Use of 

 Two New Electrical Instruments. Bij Mr. Tiberius Cavallo, F.R.S. p. 15. 

 Professor Lichtenberg, of Gottingen, some time ago made an experiment on 

 the electrophorus, an account of which was first received in London towards the 

 latter end of the year 1777. The phenomena attending the experiment are very 

 entertaining and various, but no person ever offered a satisfactory explanation of 

 them. The author himself, in his paper entitled " De nova methodo naturam 

 ac motum Fluidi Electrici investigandi Commentatio prior," where he gives an 

 account of the experiment, does not attempt any explanation of it; contenting 

 himself with the account only of various particulars attending it. Mr. C. there- 

 fore here gives the explanation. But the whole may better be consulted in the 

 2d volume of his Treatise on Electricity, in 2 vols. 8vo. 



///. yJ New Method of Assaying Copper Ores. By George Fordyce, M. D., 



F. R. S. p. 30. 



Process. — Take lOOgrs. of the ore, powder it finely, put it into a small matrass 

 or a glass phial, pour on it ^oz. of nitrous acid, of the strength commonly sold 

 by the name of aquafortis, that is, the pure acid diluted with about 4 times its 

 weight of water; and ^rOz. of muriatic acid, sold by the name of spirit of salt; 

 place the vessel in a sand heat, or if you have none, an iron pot or fire shovel 

 with sand may be set over a common fire, and the matrass or phial set in it. 

 Raise a moderate heat; an effervescence will take place for the most part; when 

 this ceases increase the heat till it is renewed, and so proceed till the liquor boils, 

 which is also to be done if no effervescence takes place; boil them together for ^ 

 of an hour. Remove the vessel from the fire, and let it cool, then pour into it 

 2oz. of water, shake them together, and let them stand till the liquor is clear; 

 pour the clear liquor into a basin where it may be preserved. Add to the 

 residuum a fresh a oz. of each of the acids, and proceed again in the same 

 manner, mixing the clear liquor with that procured by the first process. The 

 game operation is to be repeated till the fresh acids acquire no tinge of blue or 

 green. 



Dissolve -L lb. of mild fixed vegetable alkali, commonly sold by the name of 

 salt of tartar, in a quart of water. Purify the solution either by filtration, or 

 letting the impurities subside, and decanting the liquor clear into a glass vessel. 

 Pour the solution of the alkali slowly into the basin containing the fluid pro- 

 cured by the former processes, till the whole matter be precipitated from the 

 acids. 



Add, by a little at a time, as much vitriolic acid, commonly sold by the name 

 of oil of vitriol, as will re-dissolve the whole, or only leave a white powder; if 

 there should be any such powder, which is seldom the case, it must be separated 



