WAfERS from ICELAND. 123 



APPENDIX. 



In order to fhew, that fuch a fmall proportion of a vitriolic 

 fait as is contained in the Iceland waters, has not the power to 

 precipitate filver, I diflblved gr. 0.3 of exficcated Glauber's fait, 

 in gr. 2000 of diftilled water, which thus contained a propor- 

 tion of Glauber's fait rather greater than that contained in the 

 Iceland waters. I then added five drops of purified aquafortis, 

 and five drops of the folution of filver. The mixture remain- 

 ed tranfparent feveral days. I afterwards added gr. 0.7 more 

 of the exficcated Glauber's fait, without diminifhing in the 

 leaft the tranfparency of the mixture. After a few days more, 

 I added gr. 9 of the exficcated Glauber's fait. This produced 

 a diminution of tranfparency, and the fediment fubfided in a 

 few days more. This fediment being carefully collected and 

 dried, weighed gr. 0.3 ; but the clear liquor which had been 

 filtrated from it, ftill retained the greater part of the filver* 

 I therefore added to it fome pure common fait, which precipi- 

 tated all the reft of the filver, and this laft precipitate, being 

 alfo collected and dried, weighed juft one grain. 



When I examined thefe two precipitates by means of the 

 blowpipe, their qualities appeared to me fo much the fame, 

 that I fufpect the firft was produced by a fmall quantity of 

 common fait, contained imperceptibly in the Glauber's fait. If 

 there were 12 or 13 parts of common fait in 1000 of the 

 Glauber's fait, they were enough to produce the above quantity 

 of the firft precipitate ; and as Glauber's fait is prepared from 

 common fait, we can eafily underftand how a fmall quantity of 

 the common fait may remain in it. 



Q^2 For 



