o74 PROFESSOR CRUM BROWN AND DR E. A. LETTS ON 
layer is almost solid from a network of snow-white needles. The reaction 
which occurs is represented by the equation— 
| 
Br—CH,—COOH + (CH,),8 = Br—S—CH,—COOH. 
CH, 
It should be remarked that, although combination of by far the greater part 
of the two substances occurs, a certain quantity of each always remains 
uncombined.* 
For the preparation of most of the derivatives of dimethyl-thetine, the 
crude hydrobromate obtained by the above method is sufficiently pure. But if 
it be desired to obtain the pure substance, the crude product is best purified 
by pounding it in a mortar with ether, allowing the mixture to subside, pouring 
off the supernatant liquid (which contains sulphide of methyl and bromacetie — 
acid), and repeating this process two or three times. The resulting mass 
of finely powdered thetine compound (which should be quite white) is then 
rapidly dried between filter paper, and the desiccation completed by placing 
it over sulphuric acid ; or it may be recrystallised from hot alcohol.t . 
The results of its analysis are as follows :—— 
Cele on Ovi. 
SSS 
Carbon, . : . : 23°9 Zor 23°1 
Hydrogen, ; : : 4:5 4:5 +8 
Oxygen, . { : : 51-9 2 oi 
Sulphur (a), . ; 3 15°9 me 16-1 
Bromine (0), . ; : 39°8 40:0 394 
100:0 
(a) Determined as sulphate of baryta after fusion with chlorate and car- 
bonate of potash. 
() Determined as bromide of silver by precipitating the solution of the 
hydrobromate direct with nitrate of silver. 
Hydrobromate of dimethyl-thetine is a very deliquescent body. It dissolves 
with ease in hot alcohol, and, if the solution be sufficiently concentrated, 
crystallises on cooling in large transparent plates, which are apparently 
rectangular. Large and perfect crystals more than half an inch across and 
more than an eighth of an inch in thickness are easily grown. It is also soluble, 
* See pp. 607-611. 
+ It should not be boiled too long with alcohol, otherwise it decomposes slowly. 

