MM. Deville and Debray on the Preparation of Oxygen. 296 
hydrogen, and found that they had the same per-centage com- 
position, WO’, They must therefore be regarded as two iso- 
meric modifications of the same acid, of which the yed/ow is 
formed both in the moist and in the dry way, but in the latter 
case only at a Jow temperature ; while the green variety is only 
formed in the dry way and at a high temperature. The latter 
he proposes to call pyrotungstic acid, in antithesis to Scheibler’s 
acid*, which is metatungstic acid. Including the ordinary acid, 
there are therefore three varieties. 
Bernoulli has made a new determination of the equivalent. of 
tungsten, both by oxidizing tungsten, and by reducing tungstic 
acid. He obtained results varying within very narrow limits, 
which lead to the number 93:4 as that of the equivalent. 
Dumas had obtained the number 92+. 
Bernoulli finally discusses the formula of the natural tung- 
states, and attempts to show that the two modifications of 
tungstic acid also occur in nature. Le adduces a great many 
analyses of Wolfram. Most of them contain a certain quantity 
of lime and magnesia, which he considers accidental constituents. 
But in most cases a niobic acid is present—in the tungsten from 
Zinnwald 1:1 per cent. ; this is to be regarded as replacing part 
of the tungstic acid, with which it is therefore isomorphous. 
The author finally describes the mode of analysing the tung- 
sten minerals. 
Engaged in investigating the methods of working up the pla- 
tinum residues for the Russian Government, Deville and Debray 
had occasion to examine the different methods of preparing 
oxygen on a large scale. They find} that sulphate of zine, 
which, as a waste product, is now so plentiful, furnishes an eco- 
nomical source of this gas. When calcined in an earthen vessel, 
it is converted into light white oxide, which, when the sulphate 
is pure, may be used for painting. The temperature required 
for its decomposition does not exceed that necessary for binoxide 
of manganese. The other products of the decomposition are 
sulphurous acid and oxygen, which may be separated by means 
of the solubility of the former in alkalies; or the following 
method may be used, which is employed by the authors for pre- 
paring oxygen by the decomposition of sulphuric acid. 
This body at a red heat may be decomposed into sulphurous 
acid, water, and oxygen, by means of a very simple apparatus, 
consisting of a retort, of about 5 litres, filled with thin platinum 
foil, or, better, a serpentine tube filled with platinum sponge and 
heated to redness. A thin stream of sulphuric acid passes into 
* Phil. Mag. vol, xx. p. 374. t Ibid, vol. xvi. p. 211. 
{ Comptes Rendus, November 26, 1860, 
