ON ARSENIC 111 



sublimate ; and in the receiver there is found a penetrating 

 volatile sulphureous acid. 



It follows from these experiments that the acid of 

 arsenic has considerable fixity (a), and a strong attraction 

 for phlogiston, without which it cannot be reduced to 

 arsenic; whence it follows, that heat must necessarily 

 contain phlogiston, since it is capable of reducing the 

 arsenical acid (b). That it resembles metallic calxes in this 

 respect, that it is incapable of uniting with sulphur, except 

 in a reguline state, appears from the volatile sulphureous 

 acid found in the receiver (c) ; for when the arsenic has 

 attracted as much phlogiston as is necessary to that state, 

 the vitriolic acid that is extricated retains so much of this 

 principle as to form volatile sulphureous acid. That this is 

 really the case, appears moreover from the sulphureous acid 

 which arsenic, changed by sublimation with sulphur into red 

 arsenic, affords. 



SECTION VI. EFFECTS OF SALINE SUBSTANCES ON ARSENIC. 

 FIXED VEGETABLE ALKALI. 



(a) When acid of arsenic is saturated with alkali of 

 tartar, a neutral salt is obtained, which cannot be reduced 

 to crystals ; but, after being evaporated to dryness, and 

 exposed to the open air, deliquesces. This neutral salt turns 

 syrup of violets green, but produces no change on the 

 solution of lacmus. (6) But if as much acid be added as 

 shall produce no change on syrup of violets, and yet redden 

 lacmus, the solution will afford fine crystals, resembling 

 Macquer's arsenical neutral salt, both in form and other 

 properties, (c) I have kept this salt in fusion for an hour 

 in a crucible, exposed to a strong heat, upon which another 

 was luted ; after the whole had grown cold, the crucible was 



