ON GITTTA PERCHA, &C. 459 
peculiarity is, that it forms, with potash and soda, salts which 
are of very difficult solubility, so that it yields, with a solution 
of one part of carbonate of potash in 200 parts of water, a con- 
siderable precipitate. The substance which becomes yellow by 
potash could not be well determined ; it is, however, neither 
vegetable albumen, nor any other so-called protein combination. 
Properties and Composition of Caoutchouc and Gutta Percha. 
— The specific gravity of lump caoutchouc was at 20° C. z: 
0.9628 ; that of bottle caoutchouc =: 0.9454. In determining 
these, the precaution was taken to remove the adhering water 
bubbles, by subjecting the caoutchouc to the action of an air- 
pump, which was also necessary in weighing gutta percha. 
The spec, weight of the latter the author found to be zz 0.999 ; 
without this precaution, it was only zz 0.728. A specimen of 
gutta percha, mechanically purified and shaped in cakes, had a 
spec, weight zz 0.966. 
The author examined, in addition to this, various samples of 
gutta percha. One, denominated a, was in cakes of five to six 
inches thick, and was darker on the outside than in the inte- 
rior ; the second, b, was of a very loose structure, and was 
much contaminated with small stones, but agreed in colour, 
which was in general flesh-red, with a ; the third, c, was white, 
slightly inclined to brown. This last piece had been removed, 
as an impurity, from a large block of gutta percha, but was 
found to be in quality perfectly equal to the best gutta, and was 
afterwards rolled out in the manufactory of Munich, Becke and 
Co., into sheets of the thickness of paper, for address cards of 
that firm. The author obtained, moreover, a sample of the 
Getah Malabedya, imported from Palembang, and also a sample 
of gutta percha adulterated with the latter. The getah, which 
appears also to be an inspissated milky juice, is much inferior 
to gutta percha; it is imported in the form of plates of two or 
three millimetres in thickness, of a greyish colour, somewhat 
clammy to the touch, and brittle when dried. When cut, it is 
of a dirty white colour, and contains many impurities. The 
vessel in which it was contained developed, on being opened, a 
disagreeable acid smell. Treated like gutta percha, and purified 
by hot water, it was much darker than the raw substance, and 
often quite black; the smell is equally offensive, and its con- 
sistency similar to that of wax or glaziers’ putty. The gutta 
percha adulterated with the getah is of a loose structure, of a 
more greyish colour, and of smell different to that' of genuine 
gutta. 
The water in which gutta percha has been boiled (especially 
the sort a) assumes a brown colour, and reacts as an acid. 
This was also observed by Soubeiran. After inspissation this 
