ON ARSENIC 129 



upon it and boiled it ; the solution was like that of letter 

 (a). In the retort there remained a little copper which 

 was not dissolved, and the bottom of the retort was tinged 

 with brown, red, and yellow spots, which were insoluble in 

 any menstruum. (c) Copper dissolved in mineral acids 

 was not precipitated by the acid of arsenic ; but when it 

 is dissolved in vinegar a precipitation ensues. Neutral 

 arsenical salts precipitate the solution of copper in the 

 form of a blue powder, which I edulcorated, dried, and 

 exposed to a strong fire for an hour. After the mass was 

 cooled, the powder appeared to be changed into a brown 

 scoria, which had covered the whole internal surface of the 

 crucible with a yellow enamel, (d) The scoria was finely 

 powdered, mixed with a little lamp-black, and exposed in a 

 small glass retort to the fire till it melted, when a fine 

 regulus of arsenic was sublimed, and the copper in the 

 residuum was found to be reduced. 



SECTION XXVII. UPON IRON. 



(a) Iron is attacked by the acid of arsenic during 

 digestion, and at last the whole solution grows gelatinous. 

 (b) But if the digestion be performed in a close phial, so 

 that the air has no access to it, it does not grow gelatinous. 

 One portion being exposed to the open air, in a couple of 

 hours afterwards the solution was grown so gelatinous upon 

 its surface that the phial might be inverted without any- 

 thing running out of it. Another portion was mixed with 

 alkali of tartar, whence a quantity of a whitish green powder 

 was precipitated, which being edulcorated and distilled in 

 a glass retort by a gentle fire, some arsenic was sublimed, 

 and the residuum was red ochre. (c) One part of iron 

 filings was distilled with four parts of acid of arsenic. The 



