360 
SULPHURIZATION OF CAOUTCHOUC. 
gold, copper, lead and iron, act by their interposed sulphur; they 
sulphurize more or less rapidly the metallic surfaces in contact 
with them. The washers placed between the flanges of tubes used 
for transmitting steam under a pressure of 4 or 5 atmospheres, 
which are exposed consequently to a temperature of 293°-308°, 
soon lose their elasticity and become hard and brittle, owing to 
the combination which takes place between the free sulphur and 
the caoutchouc. This is greatly avoided by desulphuration with 
caustic alkaline solutions, or by the use of a new method of vul- 
canizing, described at the end oHhis paper. 
Some comparative experiments made with, 1st, normal, 2d, vul- 
canized, 3d, desulphurated caoutchouc, show that, on immersion 
for two months under similar circumstances, the absorption of pure 
water was for the first 0*200-0-260, for the second 042, and for 
the third 0-064. Some balloons, 2 millims. in thickness, filled with 
water, and submitted to a pressure which doubled their diameter, 
lost by continual transpiration in twenty-four hours, and per square 
metre, the normal caoutchouc 23 grms., the vulcanized 4 grms. 
Similar balloons, filled with air under the same pressure, expe- 
rienced scarcely any loss in eight days. The perceptible loss of 
water through a thin layer of caoutchouc will be readily under- 
stood ; the liquid introducing itself by capillary attraction into the 
pores of the organic substance, and replacing in a continuous 
manner the quantities which evaporate at the external surfaces. 
That the air and gases in general do not behave in a similar 
manner needs no explanation. 
The process of cold vulcanizing invented by M. Parkes consists 
in plunging the sheets or tubes of caoutchouc into a mixture of 
100 parts sulphuret of carbon and 2*5 parts protochloride of sul- 
phur ; the liquid, penetrating into the organic substance, causes it 
to swell, and deposit sulphur, which unites with the caoutchouc, 
owing to the decomposition of the unstable compound which it 
formed with the chlorine. The superficial parts would be too 
strongly vulcanized, and would become brittle, if care were not 
taken to remove the objects after a minute or two, and to immerse 
them immediately in water, as recommended by M. Gerard. The 
chloride of sulphur is decomposed by its contact with water, while 
the portions which have penetrated further continue their sulphur- 
