TRANSACTIONS OF SECTION E. 671 



acids, containing neither tungstic nor niolvbdic oxide, as for instance, 12V o r . 

 P 2 5 • 3Ba0 + 45 a 1-> and 20V A • PA • ' 6H 2° + 53 aq. These compounds he 

 termed phospho-vanadates ; arsenico-vanadates also occur as well as various series 

 containing vanadic dioxide, as 'well as pentoxide — a particular case being for 

 instance, 18V 2 0-, . V0 2 . 2P 2 O s . 7(NH 4 ) 2 + 50 aq. In conclusion the author 

 showed that the numerous compounds of the type, PC1 5 . SbCl 5 , long known to 

 chemists, in many cases at least corresponded to very simple forms of complex 

 acids. 



2. On an Example of Chemical Equilibrium. 

 By A. Vernon Harcourt, M.A., LL.D., F.B.S. 



3. On the Incomplete Combustion of Gases. By H. B. Dixon, M.A. 



(1) Bunsen's original experiments on the incomplete combustion of mixtures of 

 carbonic oxide and hydrogen are vitiated by the presence of aqueous vapour in 

 the eudiometer. Both Horstmann's experiments and my own show that no altera- 

 tion per saltum occurs in the ratio of the products of combustion. 



(2) A mixture of dry carbonic oxide and oxygen does not explode when an 

 electric spark is passed through it. The union of carbonic oxide and oxygen is 

 effected indirectly by steam. A mere trace of steam renders a mixture of oxygen 

 and carbonic oxide explosive. The steam undergoes a series of alternate reductions 

 and oxidations, acting as a ' carrier of oxygen ' to the carbonic oxide. "With a 

 very small quantity of steam, the oxidation of carbonic oxide takes place slowly. 

 As the quantity of steam is increased, the rapidity of the explosion increases. The 

 mean rate of explosion for one metre was found to increase from 36 metres a second 

 — when the mixture was passed over anhydrous phosphoric acid — to 317 metres 

 per second, when the mixture was saturated with aqueous vapour at 60° 0. 



(3) When a mixture of dry carbonic oxide and hydrogen is exploded with a 

 quantity of oxygen insufficient for complete combustion, the ratio of the carbonic 

 acid to the steam formed depends upon the length of the column of gases and 

 the pressure under which the gases are fired. By continually increasing the initial 

 pressure, a point is reached where no further increase in the pressure affects the 

 products of the reaction. At and above this ' critical pressure ' the result is in- 

 dependent of the length of the column of gases. The larger the proportion of 

 oxygen used, the lower the ' critical pressure ' is found to be. 



(4) When dry mixtures of carbonic oxygen and hydrogen in varying proportions 

 are exploded above the ' critical pressure ' with oxygen insufficient for complete 

 combustion, an equilibrium is established between two opposite chemical changes 

 represented by the equations : — 



(i) CO + H„0 = CO., + H, 

 (ii) C0 2 + H 2 = CO + H 2 



so that at the end of the reaction the product of the carbonic oxide and steam 

 molecules is equal to the product of the carbonic acid and hydrogen molecules 

 multiplied by a coefficient of affinity. This result agrees with Horstmann's con- 

 clusion. But Horstmann considers the coefficient to vary with the relative mass of 

 oxygen taken. 



(5) A small difference in the initial temperature at which the gases are fired, 

 makes a considerable difference in the products of the reaction. This difference is 

 due to the condensation of steam by the sides of the vessel during the explosion, and 

 its consequent removal from the sphere of action during the chemical changes. 

 When the gases are exploded at a temperature sufficiently high to prevent any con- 

 densation of steam during the progress of the reaction the coefficient, is found to 

 be constant, whatever the quantity of oxygen used, provided the hydrogen is more 

 than double the oxygen. 



(6) The presence of an inert gas such as nitrogen, by diminishing the intensity 

 of the reaction, favours the formation of carbonic acid in preference to steam. 



