Mr. Smith on the Hydrates of Nitric Acid, 455 



mencing my experiments very carefully for chlorine, and found 

 to be perfectly free from that impurity, and to have a specific 

 gravity of 1"500. 



Fourteen ounces of acid of the above-named strength were 

 mixed with 7 ounces of commercial oil of vitriol, and distilled 

 in a sand-bath over a gas flame ; the first 2 ounces that came 

 over were rejected, and the receiver changed directly the red 

 fumes of nitrous acid were observed to fill the interior of the 

 retort. The acid collected was almost as dark in colour as 

 the acid before distillation. Its specific gravity was 1*522, 

 and it turned out to be perfectly free from the smallest trace 

 of sulphuric acid. 



I also examined the first two ounces of acid that came over 

 very carefully for chlorine, and found it to contain scarcely a 

 trace, nitrate of silver producing only a slight opalescence, 

 and that which came over afterwards, being the portion that 

 I selected for my experiments, contained none at all. This last 

 acid, when diluted with water, gave off nitric oxide gas with 

 a burst of effervescence, which was the principal reason why 

 it could not be employed to ascertain the exact amount of 

 real acid by saturation in its present dark-coloured condition. 



The apparatus employed in decolorizing the nitric acid 

 consisted of a capacious retort, capable of holding about a 

 pint, to the beak of which Avas attached a large tubulated 

 receiver, which was kept surrounded with water, to condense 

 any little acid that might come over during the process ; to 

 the tubulure of this receiver was adapted a glass tube, bent 

 at right angles, fitting tightly with a cork, the other extremity 

 being in connexion with a large gas-holder, which was kept 

 constantly filled with water, to be used as an aspirator. To 

 the tubulure of the retort was also fitted a long glass tube 

 bent at right angles, the one end of which terminated within 

 an inch of its bottom, whilst the other was in connexion with 

 a couple of tubes, each 2 feet 11 inches long, arranged side by 

 side, and connected by means of a tube of a smaller diameter 

 bent like the letter U. 



These long tubes, through which the air was to be aspired, 

 were filled, the one with dried chloride of calcium, and the 

 other with pumice-stone moistened with oil of vitriol, and by 

 these means the absence of all moisture from the air was en- 

 sured. 



In decolorizing the acid a quantity amounting to 6 or 7 

 ounces was introduced into the retort, and after having ascer- 

 tained that the whole apparatus M'as perfectly tight, heat was 

 applied to the bottom of a small sand-bath in which the 

 retort was immersed, and the temperature kept up carefully 

 to 1 70° F. Then, by removing the plug at the bottom of the 



