130 ESSAY VI. 



mass made a great effervescence towards the end, and when 

 it became dry it took tire in the retort upon increasing the 

 heat, and then both arsenic and regulus of arsenic were 

 sublimed. After it was grown cool, the residuum was 

 found to be black ; it was friable, and contained but little 

 acid of arsenic. The retort was covered with yellowish 

 brown spots, (d) Solutions of iron in mineral acids are not 

 precipitated by the acid of arsenic, but iron dissolved in 

 vinegar is precipitated in the form of a dark brown powder. 

 Neutral arsenical salts precipitate all solutions of iron. The 

 precipitated powders, if exposed to a strong fire, enter into 

 fusion with an arsenical smell, and are changed into black 

 scorine, which, when mixed with charcoal powder and 

 calcined, yield copious vapours of arsenic, and are after- 

 wards attracted by the loadstone. 



SECTION XXVIII. UPON LEAD. 



(a) Lead digested with acid of arsenic turned black at 

 first. Some days afterwards it was surrounded with a light 

 greyish powder, which is mixed with a little arsenic, but 

 this may be sublimed by a gentle fire. The acid contains 

 no lead dissolved. (6) One part of shavings of lead was 

 distilled with two parts of dry acid of arsenic reduced to 

 powder. The lead was dissolved, and the mass flowed clear, 

 a little arsenic rising into the neck of the retort. After the 

 retort was grown cold, I found a milky glass in it, which I 

 boiled in distilled water, and thus a quantity of white powder 

 was separated ; the superfluous acid of arsenic was dissolved 

 in the water, (c) This powder was edulcorated, then put 

 into a little retort and kept in fusion for half an hour, but 

 no arsenic was sublimed. I put some small pieces of 

 charcoal into the retort, upon which a violent ebullition 



