Scientific American Supplement, No. 611, September 17, 1887

by Various

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.

In the remainder of this paper I have been assisted by my son Bruce, who also assisted in the experiments that I have described. He has since been engaged on the trials on a manufacturing scale; and I ask you to permit him to read the concluding portion of the paper, in which he will describe the process, and what he has done.

The process referred to in the foregoing portion of the paper is a method employed for heating the liquor, whereby a chemical action is brought into play, with the results already mentioned. This method consists in passing the products of combustion of a furnace from a clear fire in a hot state through a still containing the ammoniacal liquor. The hot gases from the furnace impart their heat to the liquor, causing the volatilization of the condensed gases, and at the same time act chemically upon the liquor and evolved gases, so that ammonia and sulphuric acid are resulting products, in the compound state of sulphate of ammonia. The formation of the ammonia produced in the process is probably due to the decomposition of nitrogenous bodies contained in solution in the liquor—the sulphocyanide, for instance; the nitrogen being given off in the form of ammonia. Of the sulphuric acid produced, we look upon the sulphureted hydrogen as the source, also any sulphites existing in the liquor, which in their volatile state take up the atom of oxygen necessary for their conversion into sulphate.

The apparatus used in working the process consists of a tower still, containing a number of superposed trays about 3 or 4 inches apart, with a lipped hole through the bottom of each at the side. The trays are so placed in the tower that the holes are at alternate sides. The liquor passes into the top of the still, and zigzags down through the series of trays, as in an ordinary Coffey still. The bottom tray differs from the rest; being much deeper, and having holes through it connecting it with the furnace, which is set immediately below it. The products of combustion of the fuel are caused to pass from the furnace up through the holes in the trays in the still, and, together with the gases evolved from the liquor, are directed into the saturator, where the sulphate of ammonia is obtained either in solution or in the crystalline state.

Where the process is at present being worked, an exhauster is used to draw the furnace gases through the still; but it might be advantageous to use a blower.

A small plant has been put in action at the gas works in Kilkenny and another on a larger scale, and differing somewhat in detail, here in Glasgow at the Alum and Ammonia Company's works, where the liquor from the Tradeston Gas Works is converted. The trials on a working scale have only been made at both places within the past ten days; and, so far, nothing has appeared against the principle, though in certain of the details of construction some alterations are being made to improve it. The extra yield of salt from a given quantity of acid obtained in the experiments has been proved in practice, as also the absorption of the sulphureted hydrogen.

The other day, while ammoniacal liquor of about 9 oz. strength was being run at the rate of 70 gallons per hour through the still, 5 feet in diameter and 10 feet high, containing seventeen trays, no smell of sulphureted hydrogen was perceptible from the waste gases from the saturator, although on applying lead paper a slight trace of this impurity was noticeable, and it may be stated that the gases were being delivered at the ground level, where there was no difficulty in testing them.