( o.ML'OlNDS <>F CARBON WITH OXYGEN AND NITKOGEN 391 



by mixing formic acid with glycerin, because in a separate state it vola- 

 tilises much earlier, and therefore cannot be heated up to the required 

 temperature. The salts of formic acid, on being heated with sulphuric 

 acid, yield carbonic oxide. Usually, however, carbonic oxide is pre- 

 pared in laboratories, not from formic but from oxalic acid, C 2 H 2 O 4 , 

 the more so as formic acid is itself prepared from oxalic acid. The 

 latter acid is easily obtained by the action of nitric acid on starch, 

 sugar. Arc. : it is also found in nature. Oxalic acid is easily decom- 

 posed by heat ; its crystals first lose water, then partly volatilise, 

 but the greater part is decomposed. The decomposition is of the 

 following nature : it splits up into water, carbonic oxide, and car- 

 bonic anhydride, 28 C 2 H 2 O 4 =H 2 O + CO 2 + CO. This decomposition 

 is generally practically effected by mixing oxalic acid with strong 

 sulphuric acid, because the latter favours the decomposition by taking 

 up the water. On heating a mixture of oxalic and sulphuric acids a 

 mixture of carbonic oxide and carbonic anhydride is evolved. This 

 mixture is passed through a solution of an alkali in order to absorb 

 the carbonic anhydride, whilst the carbonic oxide passes on. Oxalic 

 acid in admixture with glycerin, on being heated first to 100 and 

 then to 140, decomposes in a similar manner. 



In its physical properties carbonic oxide resembles nitrogen ; this 

 is explained by the equality of their molecular weights. The absence 

 of colour and smell, the low temperature of the absolute boiling 

 point, -140 (nitrogen 146), the faculty of solidifying at -200 

 {nitrogen, -202), the boiling point of 190 (nitrogen, 203), 

 -and the slight solubility (page 78), of carbonic oxide are almost the 

 same as in those of nitrogen. The chemical properties of both 

 gases are, however, very different, and in these carbonic oxide re- 

 sembles hydrogen. Carbonic oxide burns with a blue flame, giving 

 2 volumes of carbonic anhydride from 2 volumes of carbonic oxide, just 

 as 2 volumes of hydrogen give 2 volumes of aqueous vapour. It 

 explodes with oxygen, in the eudiometer, like hydrogen. 29 When 



28 The decomposition of formic and oxalic acids, with the formation of carbonic oxide, 

 considering these acids as carboxyl derivatives, may be explained as follows : The first 

 is H(COOH), and the second (COOH) 2 , or H 2 , in which one or both parts of hydrogen are 

 exchanged for carboxyl; therefore they are equal to H 2 + CO 2 and H 2 + 2CO 2 ; but Ho 

 reacts with CO 2 , as has been stated above, forming CO and H 2 O. From this it is also 

 evident that oxalic acid on losing CO 2 forms formic acid, and also that the latter may 

 proceed from CO + H 2 O, as we shall see further on. 



29 It is remarkable that, according to the investigations of Dixon, perfectly dry 

 carbonic oxide does not explode with oxygen when a spark of low intensity is used, but 

 an explosion takes place if there is the slightest admixture of moisture. L. Meyer, 

 however, showed that sparks of an electric discharge of considerable intensity pro- 

 duce an explosion. I think that this may be explained by the fact that water with 



