375 
were possible to examine the unfermented wort. The addition 
of the hypochlorite to genuine wort does not turn it at all red, 
and merely alters it to a pale yellow ; whereas, if ealumba be 
present, it turns it to a decided red. 
Picric acid may be detected when present in no larger 
quantity than one grain to a gallon. When dissolved in water 
it is of a bright yellow colour, and cuts off the blue end of the 
spectrum in a sufficiently well-defined manner, giving the 
spectrum 84- . . . This is not changed by ammonia or citric 
acid, nor does hypochlorite of soda cause it to fade when 
added to an acid solution. The most striking change is that 
produced by the addition of sulphuric acid, which makes it 
so much paler that a couple of drops added to the aqueous 
solution in one of the small cells leaves it nearly colourless. 
In order to detect it in beer, about one ounce should be evapo- 
rated to dryness, and then redissolved in no more water than 
will make the solution sufficiently liquid to allow bubbles to 
rise readily through it. This should be introduced into a 
test tube and agitated with ether, which dissolves out the 
greater part of the picric acid, but scarcely any colour from 
genuine beer. Since it is very important to avoid contamina- 
tion with any of the material not soluble in ether, it is well, 
in the first case, to use somewhat more than the bulk of the 
concentrated beer, and to transfer it to another perfectly dry 
test tube, then agitate with a fresh quantity of ether and 
add it to the first, arranging so that the total amount of 
ether may fill a half-inch test tube to the depth of about two 
inches. After corking it up it should be allowed to stand 
till quite clear, and till any particles not soluble in ether have 
adhered to the sides of the tube. The clear solution should 
then be poured off into another tube, water added so as to 
give a depth of about half an inch, and well agitated with the 
ether. After it has collected at the bottom the ether should 
be removed by a pipette, the aqueous solution washed with a 
little fresh ether, and then evaporated to dryness. In the 
case of genuine beer the ether extracts scarcely any colour, 
and the greater part of this and the resinous matter after- 
wards remain in the ether, so that on evaporating the aqueous 
solution, which is scarcely coloured, a mere trace of a yellow 
colour is obtained, so free from resin that, when dissolved in 
water and a drop or two of alcohol added, we obtain a clear, 
very pale yellow solution, so pale that if one ounce of beer 
has been used the spectrum is about 10. . 11. — , changed to 
about 9 . . 10 - -11 — by sulphuric acid. If, however, picric acid 
be present the solution in ether is a decided clear bright 
yellow ; the greater part of the colour is extracted from it by 
VOL. IX. — NEW SER. B B 
