58 



Some more arsen. acid was calcined for a good while in a coffee cup 

 covered in the same manner, with a heat, I should imagine, sufficient to melt 

 copper ; no arsenical fumes were perceived on heating, but were very visible 

 when the crucible was taken out of the furnace ; almost all the arsen. acid was 

 sublimed : what remained seemed to have been melted, but had no appear- 

 ance of vitrification. 



Some of the arsen. acid was saturated with magnesia : the solution was 

 evaporated, but it did not seem disposed to crystallize : it presented nearly the 

 same phenom. with metallic solutions as the neut. arsen. salt. 



Some earth of alum was dissolved in the arsen. acid : it dissolved without 

 efFerv., as it does in other acids ; it did not seem disposed to crystallize ; this 

 solution made a pretty bright scarlet precip. with solut. silver, whereas the 

 neut. arsen. salt makes a sort of purphsh-red : the phenom. which it presents 

 with other metallic soluts are not remarkably different from those made by 

 the neut. arsen. salt. 



The arsen. acid itself makes much the same coloured precipitates with 

 solut. silver & mercury in nitrous acid, & of tin in spt of salt, as the neut. 

 arsen. salt : with most other metallic solutions it makes no precip. 



Neither the neut. arsen. salt nor any other combination of the arsen. acid 

 makes any precip. with solut. nickel in aq. regia, and but very little with the 

 red tincture extracted from zaffer by aq. regia, id est, a solution of regulus 

 of cobalt : even that little seems owing to the bismuth contained in it. 



EXPERIMENTS ON FACTITIOUS AIR. 



[The date of these experiments is probably not later than 1767.] 



PART IV. 



Containing experiments on the air produced from vegetable and animal siibftances 



by distillation. 



I received the air produced from these substances in inverted bottles of wa- 

 ter, nearly in the same manner as in the former experiments read to this So- 

 ciety, by means of the apparatus represented in the annexed drawing. 



Exp. 1. 400 grains of raspings of Norway oak, called wainscot by the car- 

 penters, were distilled in the above-mentioned manner, till no more air would 

 rise with a heat just sufficient to make the distilling vessel obscurely red hot. 

 The bottle in which the air was received was then removed, & another put 

 in its place, & the distillation completed with a pretty strong red heat. 

 By this means that part of the air which requires a red heat to disengage it 

 was procured separate from that which rises with a less heat. Each of these 

 parcels of air were then brought in contact with sope leys in the manner de- 

 scribed in my experiments on Rathbone-place water, in order to see whether 

 they contained any fixed airs, & to free them from it if there was any. 

 The first parcel of air, namely that which rose first in distillation, measured 

 22100 grains when first made, & was reduced by the sope leys to 12700. 



