O. Folin and W. 8S. McEllroy 515 
the mixture keeps indefinitely.4| Less than 1 gm. of the sulfo- 
cyanide, now so difficult to obtain, is consumed for each titration. 
The titrations are made in test-tubes. By this innovation 
the following advantages are gained: (1) the cost of chemicals is 
greatly reduced; (2) the preliminary heating period is very short; 
(3) there is no need for regulating the flame to some definite 
speed of boiling as this is accomplished by moving the test-tube 
sidewise through the flame; (4) the disappearance of the last 
traces of blue color is more sharply marked because the volume 
of liquid is small; (5) there is little or no return of any blue or 
green color at the end of the titration. Independently of the 
shape of vessel used for the titration the return of a blue or green- 
ish color by reoxidation is very slow in our titration mixtures. 
Using pure sugar solutions and test-tubes the titrated solutions 
remain colorless for several hours. 
The titrations are made on undiluted urine even when as 
much as 6 or 7 per cent of sugar is present. This simplification 
is made possible by attaching to the tip of an ordinary 25 cc. 
glass-stoppered burette another tip, consisting of a glass tube 
drawn out at one end to an almost capillary bore. It is a very 
simple matter, and requires only a few minutes’ work, to make 
a dozen such tips which will deliver between 45 and 55 drops of 
urine per cc. We have found these fine tips very helpful in many 
other kinds of accurate titrations; they permit the measurement 
of 4 fraction of 1 ce. with almost as great an accuracy as the 
measurement of 5 cc. with an ordinary burette. 
The burettes carrying accessory tips are most conveniently 
filled by suction instead of by pouring in the urine from the top. 
This mode of filling the burette avoids all spilling of urine, all 
foaming within the burette, and all waiting for the meniscus to 
reach the proper level. The filling of the burette by suction has 
also the advantage that it eliminates the necessity of rinsing the 
burette with the sugar solution or urine to be titrated. A 5 per 
cent urine can be used directly after a 0.5 per cent one, or vice 
versa. That this is the case can be shown by filling the burette 
with water after it has just been emptied from a urine containing 
4 When first made the salt mixture tends to cake or set a trifle. If it is 
left in the mortar or other vessel, covered with paper, over night and is 
then stirred up once more, before bottling, it does not harden again. 
