VOL. LXXIII.] PHILOSOPHICAL TRANSACTIONS. 411 



the liquor after the precipitation of the other matters hy the Prussian lixivium, 

 and been precipitated by the alkali added at last. 



Exper. Q. On precipitating a like solution by gradual additions of alkaline 

 lixivium, and separating the precipitates as often as a fresh addition of the alkali 

 occasioned any different appearance from what the preceding had done ; the first 

 precipitate was white ; the next of a rusty red colour, like precipitate of iron ; 

 the last very white, while diffused through the liquor, and when settled, but in 

 drying turned a little brown. The first, which was in a very small quantity, as 

 nearly as could be judged by weighing the filters, about -^v part of the other 2, 

 was found to be lead ; the 2d was iron ; and the 3d manganese, nearly in equal 

 quantities, all pure, or very nearly so, from each other. 



It appears from these experiments, that 22 parts of this mineral contain nearly 

 two of indissoluble earth, chiefly micaceous, 1 of lead, about 94 of iron, and 

 the same quantity of manganese. 



Specimens of the colours produced by vitrification. — o. The mineral itself. 

 1. 2. 3. The first, second, and third precipitates. 



XIX. On the Method of preparing, with, the least possible loss, pure and white 

 fusible Salt of Urine and perfectly transparent Phosphoric Acid. By the Duke 

 de Chaulnes, F. R. S. p. 288. From the French. 



Until of late years, phosphoric acid was prepared from the so called fusible 

 salt of urine, a triple salt consisting of soda and ammonia united to the phos- 

 phoric acid.* This fusible salt was obtained by evaporating urine, dissolving 

 the saline residuum in distilled water, filtrating the solution, and then evaporating 

 and crystallizing ; and purifying it, by re-dissolving and re-crystallizing; during 

 which operations much of the salt was commonly lost. In this memoir, the 

 duke de Chaulnes shows in what manner, with the least possible loss, a pure and 

 white fusible salt of urine, and a perfectly transparent phosphoric acid, may be 

 obtained; but as these processes, which require much time and trouble, have 

 been wholly set aside by Scheele's easier and more certain method of procuring 

 phosphoric acid from bones, it is unnecessary to take up the reader's attention 

 with a further account of this paper. 



*XX. Experiments for ascertaining the Point of Mercurial Congelation. By 

 Mr. Thos. Hutchins, Governor of Albany Fort, in Hudson's Bay. p. *303. 



The following experiments, to determine the freezing point of quicksilver, 

 were made by the direction of the r. s., at Albany Fort in Hudson's Bay, situ- 

 ated in the lat. of 52° 14' north and 82° west long, from Greenwich. The in- 



* Phosphate of soda and ammonia. 

 3 a 2 



