42 ESSAY IV. 



of the earth with sal ammoniac, to a gentle evaporation in 

 a slightly covered glass vessel. The product was 1 drm. 

 5 6 grs. of an ammoniacal salt ; the glass did not appear to 

 haVe been attacked. 



I sublimed half a drachm of this salt in a small retort, 

 which, towards the end of the operation, I laid upon the 

 bare fire. No crust appeared upon the surface of the water 

 in the cover. At the bottom of the retort lay a little 

 flocculent earth, of a light grey colour, above which the 

 internal surface was covered with a white pellicle that 

 reflected various colours, and in the neck there w r as a 

 sublimate. 



The thin pellicle easily separated in many places from 

 the glass, which was quite smooth beneath, though it was 

 not without small furrows. 



I poured water both upon the ammoniacal salt and 

 the crust, in consequence of which it acquired a very sour 

 taste, and coloured the tincture of turnsol red. 



The white crust that was left undissolved behind 

 weighed 5 grs., and under the blowpipe ran without addition 

 into a green glass. This was nothing but the glass that 

 had been corroded by the fluor acid ; but, as this acid can 

 be set loose only by a strong heat, it had done no more 

 than corrode the glass, without passing over along with it 

 in the form of vapour, and then depositing it again on the 

 water. For, upon pouring 2 drms. of oil of vitriol upon 

 half a drachm of this ammoniacal salt, a little moistened, 

 and placed in a glass retort, a great foam arose, and the 

 thick vapours that ascended covered the water in the 

 receiver with a white crust. 



A scruple of the salt on solution left behind 1 gr. of 

 earth, which, as I conjecture, it had taken up during the 

 evaporation in the glass vessel. 



