Prof. Dixon and Mr. Smith on 



of original detonating gas unburnt : — 



Maximum ... ro8 



•92 

 Minimum "69 



Mean '88 



V07 



With regard to the calculation of the amount of unburnt 

 detonating gas, a slightly different method is employed,, 

 according as the original gas contains excess of oxygen 

 or hydrogen. All the residues contain a certain percent- 

 age of nitrogen, part of which is due to inleakage of air,, 

 and to air in the CO2, used for sweeping out the tube, whilst 

 part exists as impurity in the original gas, being chiefly 

 derived from the water in the gas-holder. It is, however^ 

 impossible to determine accurately how much is due to each 

 cause. In calculating the percentage of unburnt detonating 

 gas, a maximum and minimum are taken in the following 

 way. Firstly, assume all the nitrogen was present in the 

 original gas, and calculate all the oxygen as belonging to 

 the unburnt residue. This gives a maximum value for the 

 percentage unburnt. Secondly, assume that all the nitro- 

 gen got in (as air) after the explosion, and from the 

 percentage of oxygen, deduct the amount of oxygen 

 corresponding to the nitrogen (as air). In this way we get 

 a minimum value for the amount of unburnt detonating 

 gas, and the true percentage must lie between these limits. 

 If there is a sufficient excess of oxygen, we get only one 

 value for the unburnt residue, viz., i j^ times the residual 

 h37drogen. It will be observed that each of the residues 

 contains a small percentage of carbonic oxide. Part of 

 this is probably due to the grease used for the taps, and 

 part may be due to hydrocarbons derived from the zinc, 

 used in the preparation of the hydrogen (except in cases 

 where electrolytic gas was used). The carbonic oxide, 

 being a combustible gas, must be taken into account in 

 calculating the residual detonating gas. When there is an 



