170 PHILOSOPHICAL TRANSACTIONS. [ANN O 1782. 



pleased to see he had thus succeeded in shortening the process. Nevertheless he 

 perceived that the acid thus obtained had somewhat of a sulphureous smell 

 whence he suspected that (contrary to Beaume's assertion, Chym. Exper. 1, p. 

 365) by the strong degree of heat employed in the process, some of the vitriolic 

 acid had been expelled from the alum. He therefore resolved to employ the ol. 

 vitrioli, as in that case a less degree of heat would be required. 



Exper, 61. On 3 parts of the saline mass * pour 1 part of oil of vitriol; an 

 extrication of grey fumes, with the smell of the acid of fat, will immediately 

 follow: a gentle heat is sufficient for disengaging all the acid; for when a greater 

 degree of heat is applied nothing is forced over into the receiver except a few drops 

 of a reddish brown oil. 



To ascertain whether the acid of fat thus procured was contaminated with vi- 

 triolic acid, Dr. C. added some of it (the acid of fat) to a solution of saccharum 

 saturni; it threw down a precipitate which was not redissolved on adding wine- 

 vinegar, even when boiled and digested therewith. Having thus detected an ad- 

 mixture of vitriolic acid, he thought it might be separated from the acid of fat, 

 by distillation with a fresh quantity of the saline mass; in which case the vitriolic 

 acid uniting with the alkali, would disengage the acid of fat.-}- 



Exper. 62. Accordingly, to 4 oz. of the obtained acid he added a fresh portion 

 (amounting to 1 oz.) of the saline mass, and distilled with a gentle heat. There 

 passed over into the receiver a colourless smoking acid, some of which being added 

 to a solution of saccharum saturni, it did indeed throw down a sediment, but 

 this sediment was redissolved on adding wine-vinegar. 



Exper. 63. Wishing to see how this concentrated acid would act on metals, 

 he digested 4 gr. of gold, precipitated from its solution in aqua regis by vitriol of 

 iron, in 1 oz. of the acid. — Another quantity of the acid was digested with gold- 

 leaf; a third quantity with 4 gr. of platina; and a fourth quantity with silver leaf. 

 In these exper. the acid which was before colourless, acquired a gold-colour. 

 This he at first supposed to be owing to the actual solution of some particles of 

 gold; but when he observed the same phenomenon to occur when the acid was 

 digested with silver, he was then led to suspect that this change of colour was 

 produced in the acid by the degree of heat alone. 



Exper. 64-74. He distilled the colourless acid perse 8 different times. That 

 portion which rose up into the receiver was pellucid, but the other portion in 



* The following are the best proportions: to $ of the saline mass, exper. 59, note*, add 4 J oz. of 

 oil of vitriol; to the remaining \ of the saline mass add the distilled acid, in order to rectifj it. 

 In this manner about 5 oz. of colourless smoking acid may be obtained. 



+ If this method be adopted, even pearl ashes may be used for making the soap; for by distilling 

 the obtained acid over a fresh quantity of the saline mass, every kind of mineral acid mixed with the 

 acid of fat, will be left behind in the said mass. 



