3l'l PREPARATION OF ANHYDROUS SULPHURIC ACID. 
I am induced to describe the arrangement that was adopted, 
for the guidance of those who may wish to prepare a spe- 
cimen of this interesting compound. 
I first obtained some highly concentrated oil of vitriol, by 
heating commercial oil of vitriol in a retort until a consider- 
able portion of weak acid had distilled off, and that which 
remained in the retort had acquired a density of 1.845. 
Some anhydrous phosphoric acid was then made by burn- 
ing phosphorus beneath a receiver placed over a plate of 
glass, allowing free access for dry atmospheric air. The 
successive portions of the white flakey substance thus form- 
ed were immediately transf^red to a wide-mouthed stop- 
pered bottle, until a considerable quantity of it was col- 
lected. 
On mixing these two acids (SO3 HO and PO5) together, 
strong chemical action, accompanied by great elevation of 
temperature, occurs, to counteract which, it is necessary to 
make the mixture in a vessel surrounded by a freezing 
mixture. 
The phosphoric acid was introduced into a stoppered re- 
tort, surrounded by a mixture of pounded ice and salt, and 
the oil of vitrei was gradually added, allowing the tempe- 
rature to subside between the successive additions. When 
a quantity of oil of vitriol, equal to about two-thirds the 
weight of the phosphoric acid, had been thus added, the 
mixture, which acquired a dark-brown colour, was removed 
from the cooling bath, and a receiver was placed there, to 
which the retort was adapted. A gentle heat was now 
applied to the retort, and dense white vapours soon began 
to pass into the receiver where they were condensed by the 
cold. In this way a considerable quantity of beautiful 
white silky crystals was obtained. The whole process oc- 
cupies but a short time, and no other precaution is neces- 
sary in conducting it, than that of avoiding too great an 
elevation of temperature on mixing the oil of vitriol with 
