The results surprised me; and being uniform over a number of experiments, pleased me.  Still, I preserved the character of a critic and said:  “I should like to treat 8 oz. of acid in the ordinary way—­saturating it with ammoniacal liquor, and then crystallizing it.”  “Oh!” Mr. Croll said, “we know what that will produce.”  I replied:  “Yes; but I would like to do it with the precise acid and liquor we have been using, so that we may have the experiment on all fours with yours, barring your process.”  These experiments were made at his country residence.  I was staying there for the night.  So next morning I got down before him, went at my experiment, saturated 8 oz. of acid (and a nice smell I made) out in the grounds, treated it afterward by division into four parts, filtered and crystallized it, all as before, with the result that I obtained 23/4 oz., as against his 31/2 oz.—­or in the proportion of 271/2 cwt. of salt to the ton of acid, as against his 321/2 cwt.

I now thought of business.  “What is the royalty to be?” I said, as we sat at breakfast.  This we settled as we Scotch say “in a crack,” or as an Englishman would say “in a jiffy.”  Mr. Croll decided to have the apparatus put up on a manufacturing scale here in Glasgow; and I determined to erect similar apparatus at one of my gas works.

I dare say that it will be uppermost in your minds, Whence comes the increased yield of salts?  Well, I will state one fact, and leave you to ruminate on it, namely, by Mr. Croll’s process we did not seem to produce any sulphureted hydrogen.  The experiments were conducted in a room with ordinary doors and windows, but without a chimney; and we were not troubled with any offensive smell—­a state of things that could not possibly have existed had we been experimenting with any other apparatus hitherto employed in the manufacture of sulphate of ammonia.  The apparatus, which will presently be described, only substitutes, for the present mode of distillation, a new one, which forms the subject of Mr. Croll’s patent.  All other parts of present apparatus can remain as they now exist.

Mr Croll has also introduced another mode of producing sulphate of ammonia, which dispenses with all the apparatus hitherto in use after the distillatory portion, and produces the salt in a state fit for the farmer, ready to be put on the land.  This process consists in sending the products of distillation through a vessel filled with wood sawdust saturated with sulphuric acid.  The ammonia becomes fixed and crystallized in the sawdust, and is ready for use.  There are many works, both at home and abroad, to which the conveyance of sulphuric acid is both difficult and expensive, on account of the cost of carriage and the breakage which occurs; and thus in many such works the ammonia is not utilized.  This saturated sawdust process will, I think, remove the difficulty; for I find that dry sawdust absorbs double its own weight of sulphuric acid, and this could be conveyed in the most ordinary casks in a damp state, and save all waste and annoyance from breakage of bottles.  In this state it could be used by the farmer, or the sulphate of ammonia could be washed out, crystallized, and exported in the state of salt.