1040
GAS.— Residual Products.
Residual Products .—In the present economy ofgas manufacture the value of the substances pro-duced at the same time as the gas is a most importantmatter. Prom being originally an absolute source ofnuisance, many of these residual products have nowbecome of considerable commercial value. The so-called “ gas or ammoniacal liquor ” is the source ofmost of the ammonia salts to be met with in com-merce ; while the tar has acquired value for the pro-duction of the aniline colours, and also as a sourceof carbolic acid, which is largely in use at thepresent time for disinfecting purposes.
The principal use of the ammoniacal liquor is inthe preparation of crude ammonium sulphate, whichis employed for agricultural purposes as a manure ;it is also to a minor extent the source of the purerammonia salts. The treatment of the liquor for thispurpose constitutes a distinct and remunerativebranch of manufacture. The actual process em-ployed has been already noticed in the article onAmmonia in the present work, to which referenceshould be made for further details. The commercialvalue of “gas liquor” is determined by the numberof ounces of strong monohydrated sulphuric acid(II 2 S0 4 ) required for the neutralization of 1 gallon,the result being expressed as so many “ ounce ”liquor. This method of valuation is defective intaking no cognizance of the ammonia present in acombined form not decomposable by dilute acid.This amount is variable, but is always a very appreci-able quantity. Distillation of the liquor with analkali, and the condensation and estimation of theammonia liberated, is the only trustworthy method,and this mode is now being adopted in place ofthe older system. Coal tar is treated in order toobtain a variety of substances, all of which have acommercial value (see Coal Tab Distillation).Of the other bye products of a gas works, cokealways commands a ready sale, while for breezethe demand is more variable, and the value con-considerably less. Spent oxide is not at presenta source of revenue to gas companies, but theterms upon which it is supplied and removed axe amatter of consideration. The cause of these favourableterms is understood when it is considered that fouloxide will often contain from 40 to 55 per cent, offree sulphur, a very appreciable quantity of impureammonia salts, and some Prussian blue , productswhich, if extracted, are readily saleable. Gas lime,foul lime from the purifiers, is not only in manycases absolutely unsaleable, but is frequently a sourceof considerable nuisance to the companies of London and other large towns. In the country the spentlime is in demand among the neighbouring farmersfor manurial purposes.
The aggregate value of the whole of the residual
products of a gas manufactory at the present time maybe taken at about one half the cost of the original coal.In order better to illustrate this, and also to help thereader to form some idea of the individual value ofeach bye product, we take as an example a condensedstatement from the published accounts of the Com-mercial Gas Company for the half year endingJune 30, 1875. The total amount of coal carbonizedamounted to 48,380 tons, of which 43,929 tons werecommon coal, and 4451 tons cannel; this yieldedresidual products as follows :—
Coke (chaldrons of 36 bushels),. 44,838
Breeze, “ *■ . 5,425
Tar (gallons),. 435.182
Ammoniacal liquor (butts of 108 gallons),. 8,653
Of these amounts the quantities sold and valuesreceived were as follows:—
Sold. Value received.
£ s. D.
Coke (chaldrons),. 34,261 .... 15,240 13 5
Breeze, “ . * 6,024 .... 18 18 7
Tar (gallons),.. *441,182 .... 3,914 7 3
Ammoniacal liquor,. 8,468 .... 2,838 12 9
22,012 12 0
* The slight excess over the quantity made was probablydue to a small amount being in stock at the commencementof the half year,
The cost of the coal was about £46,900, includingdues, &c., and the realized value of the residualssold £22,012 12s., after deducting cost of labour andcartage for the breeze and coke; as, however, thequantity of coke sold was less than the quantityobtained by about one-fifth (this amount havingbeen used in the retort furnaces), it will be seenthat the total value of the residual products in thiscase was considerably more than one-half the cost ofthe original coal. From an analysis of the aggregatefigures the realizable value of each residual expressedin minor terms is as follows:—
Breeze, “ . 0 OJ
Tar, per gallon,. 0 2
Ammoniacal liquor, per butt,. 6 8J
There is little doubt that the large gas companieswill turn their attention more and more in thefuture to the proper valuation, as well as the moreprofitable utilization, of these residual products.A small increase of plant would enable a gas com-pany to turn its own ammoniacal liquor into themore saleable and convenient form of ammonia salts,the doing of which would undoubtedly be profitable.
Improvements in this direction will in the longrun be to the advantage of the gas company, andalso to the gas consumer.
END OE VOL. 1.