578 PROFESSOR CRUM BROWN AND DR E. A. LETTS ON 
time in a water bath, and from time to time tested with freshly precipitated 
oxide of silver. When this ceases to be affected, the mixture is filtered, and 
the small quantity of silver contained in solution * removed by the cautious 
addition of hydrochloric acid. The solution is again filtered and concentrated 
on a water bath till it is syrupy, and then placed in a desiccator. After some 
time (usually a day or two) large crystals of the base separate. These may be 
purified by re-crystallisation from boiling alcohol. 
Hydrated dimethyl-thetine is a colourless substance which may be obtained 
in large crystals. It is very hygroscopic, and hence crystallises with difficulty 
from an aqueous solution ; but although soluble to a considerable extent in 
alcohol, it is much less so in that liquid than in water, and readily crystallises 
on cooling its saturated alcoholic solution. . 
Its composition was determined by combustion with oxide of copper. The 
numbers obtained are as follows :— 
Calculated for Obtained. 
C,H, S803 plum, 
Carbon, ; : ; 34-7 34-0 0 33°9 
Hydrogen, . : ; 72 73 73 
It has a taste which is at first slightly burning—afterwards saline. It is 
neutral to litmus. 
As might be expected, it is but a weak base, and does not combine with 
carbonic acid—indeed, it may be obtained by the action of carbonate of barium 
on its sulphate, carbonic acid escaping. Attempts made to prepare its cyanide 
were also unsuccessful, hydrocyanic acid being evolved when solution of the 
hydrobromate was mixed with cyanide of silver, and the base remaining on 
concentrating the solution over sulphuric acid. 
The hydrated base does not lose water when placed in a desiccator over 
sulphuric acid. Heated to 100°C. it decomposes.+ But if it be placed in vacuo 
over sulphuric acid it swells up, becomes opaque, and loses a molecule of water, 
becoming transformed into the anhydrous base— 
CH,—COO0:H CH,—CO 
CH, 0H =a 
| | 
CH, CH, 
It is quite possible, however, that the formula of the anhydrous base is 
double that of the above, as in the case of glycocol, &c., viz.— 
* This silver was probably dissolved by the free bromacetic acid contained in the crude hydrobnoumig 
employed for the preparation of the base. 
+ Its products of decomposition are described in a separate paper. See page 598. 

