Chemistry and Physics. 155 



siderable. The completeness of the combustion was verified by 

 an examination of the products. The heat of combustion thus 

 obtained is of course the heat at constant volume. For carbon 

 this is the same value as that at constant pressure, since the car- 

 bon dioxide formed replaces the oxygen volume for volume. For 

 hydrogen compounds, however, the usual corrections are neces- 

 sary for the condensation of the water vapor. When cellulose in 

 the form of cotton was burned in this way, the ash being de- 

 ducted, one gram gave 4*2 calories ; or one equivalent (162 

 grams) 680'4 calories. The heat of combustion calculated at 

 constant pressure, the water being in the liquid state, is 681*8 

 calories. Comparing this value, with that of the carbon con- 

 tained in the cellulose (referred to diamond) 564 calories, it ap- 

 pears that that of the cellulose is in excess 117*8 calories, or 

 about one-fifth. It follows from this that the hydrates of carbon, 

 so-called, contain an excess of energy above that given by the 

 carbon and water which their decomposition would furnish. The 

 authors call atteution to the fact that this is also true of incom- 

 pletely burned chai*coal, as for example the charbon roux used in 

 making gunpowder; and hence that the energy of a sample of 

 gunpowder due to the carbon it contains cannot be accurately 

 calculated from its percentage composition. — Bull. Soc. Ch., II, 

 xliii, 262, March, 1885. g. f. b. 



3. On a new absorbing agent for Oxygen. — Von der Pford- 

 ten has suggested the use of chromous chloride as an absorbing 

 substance for oxygen. To prepare it, chromic acid is heated 

 with hydrogen chloride until the liquid is perfectly free from 

 chlorine. The green solution of chromic chloride is then reduced 

 by means of zinc, to the blue solution of chromous chloride. 

 This is then poured, in an atmosphere of carbon dioxide, into a 

 saturated solution of sodium acetate, whereby a red precipitate 

 of chromous acetate is produced, which is washed by decanta- 

 tion with carbonic acid water. The precipitate is quite perma- 

 nent and may be preserved for some time without change in 

 closed vessels filled with carbon dioxide. For use it is converted 

 into chromous chloride by placing it in a test-glass closed bv a 

 rubber stopper bored with three holes. Through one of these a 

 funnel passes, furnished with a cock. The others have entrance 

 and exit tubes as usual. When the air is displaced by carbon 

 dioxide, the acetate is placed in the glass in excess, the gas 

 stream continued and hydrochloric acid allowed to flow in and 

 convert it into a blue solution of chromous chloride. When a 

 gas containing oxygen is passed through it the color changes 

 from blue to green. Experiments have shown that an alkaline 

 solution of pyrogallol is entirely unaffected by gas which has 

 passed through the solution of chromous chloride. Hence, 

 hydrogen, carbon dioxide, hydrogen sulphide and the like may 

 be freed from oxygen in this manner. — Liebig Ann., ccviii, 112, 

 March, 1885. g. p. b. 



