Dr. Mitchell’s apparatus, the capacity of the receiver is about one fourth 
of that of the generator, which is probably so Lied occasion con- 
siderable loss in this way... 
~ Bat it is important also that there didi cidinindnnenrin 
the generator, or in other words, that the materials. used to charge it, 
should very nearly fill_it. After introducing the vessel of sulphuric 
acid and inserting the plug, there must of course remain a little space 
filled only with air ; and this probably is necessary, for after chemical 
action takes place, the several substances formed appear to’ occupy a 
little more space than before. But if possible, the quantity of soda, 
&e. used, should be such that the sulphate of soda which is formed, and 
carbonic acid in the liquid state, should entirely fill the generator. If 
then the receiver is of the proper capacity, after the liquid acid is dis- 
tilled over into it, there will ‘remain only the space it previously oceu- 
pied in the generator to contain the gaseous acid, which of course must 
be lost; but this is the least loss which the nature of the case admits of. 
~ When our apparatus was first constructed, (the generator of which 
holds five pints,) we were accustomed to use at a charge two pounds 
of the bicarbonate, and sulphuric acid’ and water in proportion, from 
which we obtained but a very little of the liquid in the bottom of the 
receiver; but upon increasing the quantity to two and a half pounds of 
soda, with sulphuric acid, &c. in proportion, we were at first a little sur- 
prised to see the liquid come over until the receiver was entirely full, 
and with such rapidity as to leave the impression upon the mind, that 
more might have been obtained if the receiver had been a little larger. 
Once or twice only we have made use of two charges of two ponnds 
of soda each, condensing the whole of the liquid acid obtained into the 
receiver, which, however, was then scarcely filled. If therefore we 
may put confidence in these results—and we believe they may be relied 
on—we arrive at this conclusion, that two and a half pounds of the 
bicarbonate of soda, with sulphuric acid, &c. in proportion, used at a 
single charge in an apparatus of the capacity of ours, will afford quite 
as much or more liquid carbonic acid, than five pounds of soda, &c. 
used at two separate charges. 
_ The third point mentioned above as requiring attention, is the differ- 
ence of temperature between the receiver and gencrator during the 
distillation of the liquid acid into the receiver. This may be accom- 
plished either by heating the generator or cooling the receiver, but the 
ene the best method. Dr. Torrey informs me that he has 
sometimes surrounded the receiver with a powerful freezing mixture, 
with lesley effect. pad ial even unite the two mutliels using 
but us pressure of the gas eS SO 
rapidly with the in fniisiretioe of temperature, that it can scarcely be con- 
sidered safe to eis heat to any part of the apparatus. 
Laie 
