The paper I have to lay before you describes the last product of the brain of one of your past presidents—­Alexander Angus Croll—­in connection with our industry.  It may not be so well known to some of the younger as it is to many of the older members of the Institute that the fertile brain of Mr. Croll has done much for the improvement and the extension of the gas industry.  I consider that he has been the most successful pioneer both in the cheapening and the purification of gas—­two elements without which our industry would progress but slowly if at all; and the success which has crowned his efforts, to our advantage, has reflected itself favorably on himself, showing by his financial success that he has also been a good man of business.  All these are conditions which enhance the value of this paper.  In the present instance, I claim no other credit than that of being the mouthpiece of Mr. Croll, whose assistant I was for ten of the busiest and most important years of his eventful life; and having (with my son Bruce) taken part in the experiments, I have been asked to describe the process to the Institute.

The manufacture of sulphate of ammonia, as hitherto conducted, has consisted either in bringing together sulphuric acid and ammoniacal liquor or in distilling the liquor by external heat, or by the introduction of steam, and bringing it into contact with the acid in the form of gases and vapor of water.  In either case a large volume of noxious gases is given off, the chief of which, being sulphureted hydrogen, has to be fixed by another method, in order to comply with acts of Parliament for the prevention of nuisances.

By the processes hitherto used, we sometimes get only 11/4 tons of salts to every ton of acid used; while in the more perfect forms of apparatus, we may get 1-1/3 tons of salts.  By Mr. Croll’s process, however, we get an increased yield of salts on the acid used, as follows:  The experiments were made with sulphuric acid of the specific gravity of 1838, or nearly concentrated oil of vitriol; and the quantity used was 8 ounces in each experiment.  The ammoniacal liquor was of uniform strength throughout all the experiments, being kept in a corked jar; and the solution of sulphate of ammonia was passed through filter paper before being crystallized.  Thus we obtained a white salt.  In each experiment the solution of sulphate was divided into four equal parts by weight, and one part filtered and crystallized to dryness over a spirit lamp; the weight in each experiment being as nearly as possible the same, or 31/4 oz. of salt to 2 oz. of acid—­being in the proportion of 26 oz. of sulphate to 1 lb. of acid, or 321/2 cwt. of salts to 20 cwt. of acid.