51 



usually called inflammable, as you fell me you have tried yourself." It has 

 been twice written over, and is founded on a note-book of experiments, the 

 date of which is given by the following extract from the 27th page of the 

 note-book, after the experiment (page 10 of the paper) on the solution of 

 arsenic in aqua fortis. 



" I-IO-O of purified spts of salt, 2 by measure, diluted with ^ the quantity 

 of water, was put into a piece of flor. flask and heated; 2-8 '0 of arsenical 

 liquor was poured into it by degrees whilst hot : it efFervd & discharged 

 fumes as usual, it seemed almost but not quite suflSce. to saturate the acid : 

 the liquor being evaporated gave crystals of sal Sylvii mixed with nitre. See 

 p. 53, infra, P. 9- 10. 



"Dec. 1764. Into some of this arsenical liquor was dropt some spt salt : 

 it caused red fumes & turned the liquor rather blue, but, as well as I can 

 judge, not near so much so as at first."] 



Experiments on the solution of Arsenic in f. Alkali. 



P. 3. The arsen. is precipitated from these solutions, according to Macquer, 

 by any acid whatsoever, which as far as I have tried agrees with my own ex- 

 periments : there is however a remarkable difference between the mineral 

 acids in this respect ; for if you take any combin, of arsen. & f, alk. in 

 which thef. alk. bears a considerable proportion to the arsen., & dilute it with 

 a moderate quantity of water, & then drop into it some oil of vitr, or aqua 

 fortis, the arsen. is not immediately precip. ; but in a day or two the bottom 

 and sides of the glass will be found coated with small crystals of arsen. ; part 

 of the arsen. however remains suspended so strongly as not to be separated 

 without crystallizing the neutral salt : whereas if you drop spt of salt into 

 the same solution, or even one diluted with a much larger quantit}' of water, 

 the arsen. is immediately precip. in white clouds. 



P. 4. Arsenic, as was before said, does not begin to efferv. with f. alk. with- 

 out a greater heat than one can bear one's hand in ; it also seems to require 

 a much greater heat than that of boiling water to deprive the alcali entirely of 

 its air. Sulphur also cannot unite to a f. alk. saturated with air without de- 

 priving it of some of it, which it is not able to do without a greater heat than 

 that of boiling water ; for which reason there is hardly any impregnating the 

 milder sorts of fixed alcalies strongly with sulphur merely by boiling together : 

 with the heat requisite to make liver of sulphur by fusion it is able to deprive 

 the f. alk. of a great deal of its air, as appears from the frothing or efterv. du- 

 ring mixing : it however cannot entirely deprive it of its air by that heat, as 

 the liver of sulphur made by fusion always makes some efferv. with acids, 

 though not so much as the f. alk. by itself. 



Experiments on the neut. arsen. salt. 

 1st process for neut. arsen. salt. 

 P. 5. 20'0"0 of nitre was well mixed with the same quantity of arsen., Recom- 

 mitted to distillation in a retort in reverb., the neck of the retort being luted 

 into a glass tube whose end was immersed into 20-0-0 of a strong solution of 

 pearl ashes ; the vapours passed through the f. alk. in the form of red fumes 



D 



