COMPOUNDS OF CARBON WITH OXYGEN AND NITROGEN 385 



HC0 2 H, acetic acid, CH 3 C0 2 H, . . . stearic acid, C 17 H 35 , CO 2 H, cfcc. 

 The double substitution will give bibasic acids, C B H 2B (CO 2 H)(CO 2 H) ; 

 for instance, oxalic n=Q, malonic w=l, succinic acid n=2, &c. To 

 benzene, C 6 H 6 , correspond benzoic acid, C 6 H 6 (CO 2 H), phthalic acid 

 (and its isomerides), C 6 H 4 (CO 2 H) 2 , up to melitic acid, C 6 (CO 2 H) 6 , in 

 all of which the basicity is equal to the number of carboxyl groups. As 

 many isomerides exist in hydrocarbons, it is readily understood not 

 only that such can exist also in organic acids, but that their number 

 and structure may be foreseen. As in hydrocarbons the hydrogen may 

 be replaced by chlorine, hydroxyl, &c., evidently the same is possible 

 with organic acids. And, therefore, the number and transformations of 

 such compounds are exceedingly great. This complex and most interest- 

 ing branch of chemistry is treated separately in organic chemistry. 



Carbonic Oxide. This gas is formed whenever the combustion of 

 organic substances takes place in the presence of a large excess of incan- 

 descent charcoal ; the air first burns the carbon into carbonic anhydride, 

 but this in penetrating through the red-hot charcoal is transformed into 

 carbonic oxide, C0 2 + C = 2CO. By this reaction carbonic oxide is pre- 

 pared by passing carbonic anhydride through charcoal at a red heat. It 

 may be separated from the excess of carbonic anhydride by passing it 

 through a solution of alkali, which does not absorb carbonic oxide. This 

 reduction of carbonic anhydride explains why carbonic oxide is formed 

 in ordinary clear fires, where the incoming air passes over a large 

 surface of heated coal. A blue flame is then observed burning above 

 the coal ; this is the burning carbonic oxide. When charcoal is 

 burnt in stacks, or when a thick layer of coal is burning in a brazier, 

 and under many similar circumstances, carbonic oxide is also formed. 

 In metallurgical processes, for instance, when iron is smelted from the 

 ore, very often the same process of conversion of carbonic anhydride 

 into carbonic oxide occurs, especially if the combustion of the coal be 

 effected in high, so-called blast, furnaces and ovens, where the air 

 enters from the lower part and is compelled to pass through a thick 

 layer of coal. In this way, also, combustion with flame may be 



the heats of combustion in thousands of calories, referring to the molecular weights of 

 the burning substances : 



B= H, CH 4 C. 2 H 6 C 6 H 6 



68-4 212 870 777 



KCO 2 = 69'4 225 887 766 



Thus H 2 corresponds with formic acid, CH 2 O 2 ; benzene, C 6 H 6 , with benzoic acid, C 7 H 6 O 2 - 

 The data for the latter are taken from Stohmann, and refer to the solid condition. For 

 formic acid Stohmann gives the heat of combustion as 59000 calories in a liquid state, 

 but in a state of vapour, 64'6 thousand units, which is much less than according to 

 Thorn sen. 



VOL. I. C C 



