330 PHILOSOPHICAL TRANSACTIONS. [ANNO 1783. 



grs. of real acid, whose proportion to water is not less than that of 1 to -jZg-, and 

 better if the quantity of water be still less; and hence, as with regard to copper, 

 a greater quantity of lead should be employed than is expected to be dissolved. 

 A strong heat is also requisite, and hot water should be added to the calcined 

 mass, though sparingly, as it occasions some precipitation. This metal is also 

 soluble, but in a very small degree, in dilute vitriolic acid; for it effervesces with 

 spirit of vitriol whose specific gravity is only 1.275. The calces of lead are 

 something more soluble in this acid. 100 grs. of vitriol of lead, formed by pre- 

 cipitation, contain 73 of lead, 17 of real acid, anil 10 of water. Vitriol of 

 lead, formed by direct solution, contains a large proportion of acid. 



Lead in the nitrous acid. — 100 grs. of lead require, for their solution, about 

 78 grs. of real acid, whose proportion to that of water may be as 1 to 1 1 or 12, 

 and the assistance of heat towards the end. This solution affords but 8 cubic 

 inches of nitrous air. The calces of lead are also soluble in this acid; but if 

 much dephlogisticated they become less soluble. 100 grs. of minium require 

 81 grs. of real acid. 100 grs. of nitrous salt of lead contain about (JO of lead. 



Lead in the marine acid. — 100 grs. of lead require tJOO grs. of real acid to 

 dissolve them, when the specific gravity of the spirit of salt is 1.141, and also 

 the assistance of heat, by which much of the acid is dissipated. A stronger acid 

 would dissolve more. The calces of lead are more soluble in this acid than 

 genuine lead. 100 grs. minium require 327 grs. of real acid; but white lead is 

 much less soluble. 100 grs. of horn lead, formed by precipitation, contain 72 

 of lead, 18 of marine acid, and 10 of water. 



Silver in the vitriolic acid. — 100 grs. of pure silver require, to dissolve them, 

 530 grs. of real vitriolic acid, whose proportion to water is not less than that of 

 1 to -»-, and when such a concentrated acid is used, it acts slightly even in the 

 temperature of 6o°; but for a copious solution a moderate heat is requisite. 

 This solution affords 30 cubic inches of vitriolic air. Standard silver affords 

 more air and requires more acid for its solution. The calces of silver (that is, 

 silver precipitated from its solution in nitrous acid by fixed alkalis, and well- 

 washed, but which still retains some nitrous acid), are soluble even in dilute 

 vitriolic acid, without the assistance of heat. 100 grs. of vitriol of silver, formed 

 by precipitation, contain 74 grs. of silver, about 17 of real acid, and 9 of 

 water. 



Silver in the nitrous acid. — 100 grs. of the purest silver require, for their solu- 

 tion, 36 of mere nitrous acid, diluted with water in the proportion of 1 part 

 real acid to 6 of water, applying heat only when the solution is almost saturate. 

 If spirit of nitre be much more or much less dilute, it will not act without the 

 assistance of heat. The last portions of silver, thus taken up, afford no air. 

 Standard silver requires about 38 grs. of real acid to dissolve the same proportion 



