STATE GEOLOGIST. 143 
perforated for about 12 inches. It is obvious that the pipe should noi be 
too close to the circumference of the kiln in order not to be hit by any 
lumps of material which might cling to the kiln lining. Of course there 
is little danger of this where a dry mixture is used. The pipe should be 
rinsed with a solution of borax which will produce a kind of glaze on 
the inside. If possible it is run straight out through the brickwork of 
the stack; outside of the kiln the 34-inch pipe reduces to 3g inch. Of 
course, a pipe system connected to every kiln and permitting of sampling 
the gas from any particular kiln simply by turning on _ the 
water syphon in the laboratory is most convenient, but is by no means 
necessary. This is especially true since, after the proper rate of 
feeding the coal and blowing in of the air have been established 
on the basis of gas analysis, but very few analyses may be necessary. 
Needless to say, all the pipe fittings must be made as air-tight as 
possible. 
Owing to the familiarity of the Orsat apparatus a description of 
it and the simple mode of operating it are unnecessary. With practice 
a gas analysis can be made in a very short time (about 15 minutes). 
A detailed description of the working of this instrument, together with 
the mode of sampling, etc., is found in Lord’s Metallurgical Notes, and 
other books on metallurgical or gas analysis. 
In calculating the per cent. of air corresponding to the gas analysis 
in question we must remember that the composition of the waste gases 
irom a lime or cement kiln shows an excess of carbon dioxide, due to the 
decomposition of the calcium carbonate. Any calculation, therefore, de- 
pending solely upon the carbon dioxide content shown by the analysis 
is bound to be erroneous. In order to show the relations existing between 
the air admitted and the per cent. by volume of carbon dioxide, oxygen 
and nitrogen given by the analysis, a short discussion of the principles 
governing the evolution of gases from the fuel will be found advisable. 
If the fuel used were pure carbon and no carbon dioxide from other 
sources could mingle with the gases the composition of the waste gases 
would invariably be 79 per cent. by volume of nitrogen and 21 per cent. 
of carbon dioxide, provided complete combustion took place, and no excess 
of air was admitted. If excess of air was admitted the sum of the per 
cent. of carbon dioxide and oxygen would be practically equal to the 
constant value, 21. But coal contains besides carbon, hydrogen (hydro- 
carbons) which also consume oxygen, so that the per cent. of carbon 
dioxide is correspondingly decreased. The one constant factor in the gas 
analysis is furnished by the nitrogen, which undergoes no change, being 
chemically inert, and hence it furnishes the most reliable basis for the 
calculation of the air admitted in the combustion of the fuel. The pro- 
portion of the nitrogen present in the air to the oxygen content of the 
latter is invariably in the ratio of 79:21, by volume, or for every volume 
