282 
PRESENT STATE OF THE CHEMISTRY OF GAS-LIGIITING. 
moniacal liquor after it leaves the purifiers. As far back as the year 184G Mr. Lowe 
directed attention to this, and he patented a process for effecting it. Very recently Mr. 
Iiawksley has, from independent observations, and from a chemical consideration of the 
subject, recommended a like process.* He advises that the gas should be drenched with 
ammoniacal liquor to the extent of a sixteenth of the volume of the gas. The effect of 
this is to strengthen the liquor and to remove from the gas ammonia, sulphuretted hy¬ 
drogen, carbonic acid, and the objectionable compounds of sulphur with carbon, and the 
hydrocarbons. In practice it is found that the gas thus treated never contains more 
than twelve grains of sulphur in any form in 100 cubic feet—the average being about 
nine grains and a half; and, to use the words of your president, “ it thus appears that 
all considerable gas companies may, by a very simple, and in other respects very useful 
process, remove a large proportion of the objectionable sulphur compounds which usually 
continue to exist in coal gas after it has been passed through lime or other metallic 
oxide.” 
The residual impurities—namely, the ammonia, sulphuretted hydrogen, and carbonic 
acid—are next to be removed in proper order. Washing the gas with water, or with weak 
ammoniacal liquor, and finally with water, will at once abstract a considerable amount of 
all these impurities; and although there is a prejudice with some engineers that this kind 
of purification is objectionable on account of its lowering the illuminating power of gas, 
yet, as we shall see hereafter, the prejudice is not founded on fact—excepting that the 
process undoubtedly removes such compounds as tar and naphthaline, which, though of 
high illuminating power, are nevertheless better out of the gas than in it, seeing how 
much mischief they do by subsequent deposition in the mains and service-pipes. You 
will have an opportunity of seeing at the Saltley station of the Birmingham and Staf¬ 
fordshire Gas Company, in this town, the good effect of thoroughly washing the gas 
with water or weak ammoniacal liquor before it passes to the purifiers. Mr. Young, the 
experienced engineer of the company, has-for some time past adopted this practice. The 
gas, on leaving the condensers, traverses successively three washers, or, as they may be 
more properly called, douche scrubbers; each of them is 25 feet high, 8 feet long, and 
4 feet wide; and the liquor or water is delivered into them at the rate of 1815 gallons 
an hour, the gas passing at the rate of about 66,000 cubic feet an hour. The w r ater or 
liquor flows through a pipe or jet with a very small orifice, and, dashing upon a disk im¬ 
mediately below it, is splashed out into a fine shower which meets the ascending gas. 
The rate of flow therefore is about 27j gallons for every 1000 cubic feet of gas. In this 
manner the gas is thoroughly cleansed before it goes to the purifiers, and the contrivance 
is such that no pressure is put upon the gas, for it passes through washers without fric¬ 
tion. The quantity of ammoniacal liquor which is thus obtained amounts to 44 gallons 
per ton of Staveley coal, the strength of the liquor being 4 of Twaddle, or about 8 ounces 
of sulphuric acid. Before this process was adopted, the quantity of liquor of the same 
strength was only 25 gallons per ton ; and the profit arising from the sale of the liquor 
is more than £2000 per annum in excess of the former returns. I find from an exami¬ 
nation of the gas that its illuminating power is from 15 to 16 sperm candles of standard 
quality, and that there is no loss of power by deposition in the mains—the gas, indeed, 
is absolutely free from ammonia, naphthaline, and carbonic acid, and the amount of sul¬ 
phur in any form does not exceed 16 grains per 100 cubic feet. When the gas has 
been thus washed it contains but little ammonia, so that a tray of acid sawdust in the 
purifier remains for months without being saturated. After this complete removal of 
ammonia the gas should be submitted to the action of wet lime, or, failing this, on sani¬ 
tary grounds, to oxide of iron ; and, lastly, to a few trays of dry lime to remove carbo¬ 
nic acid, which, as I shall show you directly, is a very objectionable constituent of gas, 
on account of its lowering the illuminating power. 
The order, then, of purification is :—1st, slow but complete cooling; 2nd, washing 
with ammoniacal liquor; 3rd, the removal of ammonia by water or acid ; 4th, the ab¬ 
straction of sulphuretted hydrogen by lime or oxide of iron; and 5th, carbonic acid. I 
have been particular in recapitulating all this, because of its great importance in the 
manufacture of good gas. 
We will now pass on to the proper subject of the lecture, namely, the examination of 
the chief constituents of purified coal gas. These may be classed under three heads :— 
* ‘Journal of Gas Lighting,’ vol. xiii, p, 542. 
