ADULTERATION OP POTASS A BY SODA. 217 
fully stirred. It is not at all necessary that the bitartrate of 
potassa ready formed should then be completely dissolved, 
because it does not prevent the alkali from being converted 
into bitartrate, and changed into a fine crystalline powder; 
but in order that afterwards the precipitation of the powder 
of bitartrate of potassa may take place in a very uniform 
manner, and allow of as concordant a measuring aspossible, 
it is betfer to heat and agitate the corked flask until the so- 
lution is complete; but, as I have already said, this care 
may be very well neglected, without fear of committing 
any essential error. The heated and still corked flask must 
be cooled as speedily as possible, by plunging it into water, 
or snow in winter, and stirring it briskly. It is as well, 
then, in order to obtain a crystalline powder of a very equal 
grain, to reduce the temperature of the flask and its contents 
below that of the surrounding atmosphere ; but in that case, 
it is necessary to restore their temperature to the same de- 
gree as that of the solution of bitartrate of potassa, saturated 
cold, before the experiment : this is easily done. The cork 
of the flask is then replaced by another, in which is securely 
fixed the open extremity of the measuring tube. However, 
H is necessary that neither the tube nor the cork descend 
into the neck of the flask more than is necessary, for the 
cork to be hermetically adapted to the sides of the neck, in 
order that, when the flask is inverted, it may not deposit 
crystalline powder between the cork and neck of the flask. 
The flask is then inverted, and, by shaking it, all the powder 
of bitartrate of potassa is made to fall into the tube; then 
the flask is withdrawn; it is then no longer necessary to 
take account of its contents for the test, (and the tube is 
struck on a solid body until the crystalline powder is col- 
lected into the smallest possible space,) and we may then, 
without any other operation, read on the scale the number 
of hundredths of pure carbonate of potassa contained in 
the potassa examined. 
After having ascertained in the manner described, the 
