258 Proceedings of Royal Society of Edinburgh. [sess. 
so that we might expect the formation of ethyl mercaptane by the 
action of dilute sodium hydrosulphide solution on ethyl acetate. The 
progress of such an action could be ascertained by titrating with an 
acid from time to time, an indicator being used which would indi- 
cate SH but not CHg-COO ions. After many attempts to find a 
good indicator fulfilling these conditions, I finally adopted phen- 
acetoline, the end-point with which, although not very sharp, 
is still sufficiently well defined to show the progress of the 
reaction. 
A solution of sodium hydrosulphide was prepared by dissolving 
sodium in water and passing sulphuretted hydrogen through the 
solution of caustic soda thus obtained until no more was absorbed. 
Excess of sulphuretted hydrogen was removed by a rapid current of 
hydrogen, and the solution was then brought to decinormal strength. 
50 cc. of the solution were mixed with 2*5 cc. of ethyl acetate at 
25°, and the mixture was at once titrated with decinormal hydro- 
chloric acid, phenacetoline being used as indicator. hTo marked 
diminution of titre was observed until a considerable time had 
elapsed, as the following table shows : — 
Time from beginning 
in minutes. 
1 
12 
66 
1440 
2880 
After an hour the solution had begun to turn yellow, probably 
owing to oxidation, and the yellowness increased as time went on, 
so that no accurate calculations can be based on these numbers. 
They are sufficient to show, however, that an action corresponding 
to saponification by an alkali does not take place between ethyl 
acetate and sodium hydrosulphide ; for in the former case the titre 
of the soda would have disappeared in two or three minutes from 
the beginning of the reaction under the conditions specified above. 
They also show that hydrolysis of sodium hydrosulphide into 
sodium hydroxide and sulphuretted hydrogen takes place only to a 
very small extent in decinormal solution at 25°, for the rate at 
Titre. 
4-75 
4-63 
4-55 
4-30 
3*95 
