119 
It would be of little use here to give an account.of the many 
difficulties experienced in this investigation. 
Let us, therefore, relate the modus operandi which has given 
results that were under all circumstances satisfactory, that is to say 
by which we obtained: 1. invariably the same volume of precipitate 
from the same quantity of SO,, 2. n-times a volume of precipitate 
from n-times. a quantity of SO,, 3. a volume of the precipitate 
entirely independent of the presence of mineral substances met with 
in biological fluids. 
3. Method to be followed in the microvolumetrical 
determination of SO, 
5 ce. of the fluid containing sulphate are mixed with 24 ec. of 
concentrated HCI 1:1; to this mixture are added 5 ec. of a BaCl, 
2 aq. sol. of 2.44°/,, in which 3 to 5 drops of acetone have been added. 
Sulphate and reagent are mixed at room-temperature. The manner, 
however, in which the BaCl, is added to the HCl-sulphate solution 
is of the greatest importance if we wish to obtain satisfactory 
results. If this is lost sight of, if it is added quickly in one case 
and slowiy in another, the two parallel-experiments may give em- 
tirely different results, and the microscopic investigation shows 
accordingly that the crystalline precipitate is not the same in these 
two instances. It seemed to me that this must be explained as follows: 
[f the BaCl,-sol is added slowly, there will still be free SO, in the 
fluid ‘at first. Now if we go on adding, the amount of dissolved 
SO, decreases; hence the proportion between the reagent and the 
SO, which has not been precipitated, is continually modified during 
the addition. Since the quantity of acetone materially affects the 
shape and size of the crystals most likely owing to its effect on 
the surface-tension, the way in which the BaCl,-sol. with the acetone 
are added, will likewise affect the volume of the precipitate. So 
important a part is played by the manner of adding that if in two 
parallel-experiments the BaCl,-solutions containing acetone, are seem- 
ingly added in the same way and immediately shaken, the volumes 
of the precipitate may still be different. In order to effect a rapid 
and perfect mixture we proceeded as follows: 
In a tube of thick glass a narrower one is placed having a 
content of about 5: cc. (see fig. 2). On the outside of this narrow 
tube a glass column has been melted reaching to the cork which 
may shut off the wide glass tube. Into the space between the narrow 
