THE OPERATIVE CHEMIST. 
442 
and in the grate a moderately close layer of green twigs or 
fresh cuttings of the vine is placed. The vessel is then 
filled up with the foot-stalks of grapes, commonly called 
the rape, to the top of the vessel, which is left quite open. 
The two vessels being thus prepared, the wine to be con 
verted into vinegar is poured in ; one is filled quite up, the 
other but half full. They are left thus for twenty-four hours, 
and then the half filled vessel is made quite full from the 
liquor of that which was before entirely so: this, in its turn. 
will be only half full. 
Four and twenty hours afterwards the same operation is 
repeated and proceeded in, the vessels being alternately 
kept full and half full during twenty-four hours, till the 
vinegar is made. 
On the second or third day, there will arise in the half 
filled vessel, a fermentative motion, accompanied with a 
sensible heat, which will gradually increase from day to day. 
On the contrary, the fermenting motion is almost imper 
ceptible in the full vessel ; and as the two vessels are alter 
nately full and half full, the fermentation is, by this means, 
in some measure interrupted, and is only renewed every 
other day in each vessel. 
When this motion appears to have entirely ceased, even 
in the half filled vessel, it is a sign that the fermentation is 
finished; and, therefore, the vinegar is then put into casks, 
close stopped, and kept in a cool place. 
A greater or less degree of warmth accelerates or checks 
this, as well as the spirituous fermentation. In France, it is 
finished in about fifteen days, during the summer; but if 
the heat of the air be very great, and exceed 25° Reaum. or 
88° Fahr. the half filled vessel must be filled up every twelve 
hours; because, if the fermentation be not so checked in 
that time, it will become violent, and the liquor will be so 
heated, that many of the spirituous parts on which the 
strength of the vinegar depends, will be dissipated, so that 
nothing will remain after the fermentation but a vapid 
liquor, sour indeed, but effete. 
The better to prevent the dissipation of the spirituous 
parts, it is a proper and usual precaution to close the mouth 
of the half filled vessel, in which the liquor ferments, with 
a cover made of oak wood. As to the full vessel, it is 
always left open, that the air may act freely on the liquor it 
contains ; for it is not liable to the same inconveniences, 
because it ferments very slowly.