We have already mentioned the pulp of potatoes as amongst the substances from which alcohol may be obtained; and the manufacture has been for some time past carried on in various places with great success. The apparatus and process which we are now about to describe, are both of foreign invention, and were intro duced into this country by the patentee, M. Saintmarc, of the Belmont Distillery, Vauxhall. The potatoes being first washed clean, are taken to a mill and ground into pulp. This pulp is then mixed with a large quantity of water, which takes up the chief part of the contaminating brown colouring matter, and it is then poured through a coarse sieve, which, detaining those pieces that have escaped the mill without being ground into pulp, they are rejected as ineligible for fer mentation, and applied to the feeding of pigs. The pulpy liquid thus freed from the coarser pieces, runs into a trough containing a number of small holes, and lined in the inside with a linen cloth sufficiently fine to prevent the floating particles of starch from passing through ; the water then drains through the linen, leaving the pulp and starch to settle in a mass. When it has sufficiently drained, and become solid and compact, it is removed from thence and laid upon a plastered floor, which rapidly absorbs a great portion of its moisture.
To dry it entirely, it is afterwards placed in a kiln or stove, which completes that part of the process. In the dry state the pulp may be kept uninjured for years, and may therefore be stored away for future use. The wet pulp being, however, equally serviceable for immediate fermentation, there is no occasion to dry it if the several processes in distillation can be carried forward at the time.
Supposing the pulp to be used in the dry state, it is cut, or broken to pieces, and mixed in the vat a, with sufficient hot water to bring it to the consistence of cream. The vessel b, lined with lead, and called the decomposing vessel, is then to be supplied with water to the depth of about six inches; to this, a quantity of sulphuric acid is to be added, in the proportion of three pounds of acid to every hundred pounds of dry pulp ; but only ten pounds of the acid to every hundred pounds of the wet pulp. The diluted pulp is then to be dis charged from the vessel a, through the cock into b, containing the diluted acid; steam is then to be admitted from a boiler, (not shown in the engrav ing,) by turning the cock in the pipe e, which descends to the bottom of the vessel, where it is made to issue from a steam-box ; the heat causes the mix ture to boil, and, after four or five hours' ebullition, the decomposition is con sidered complete. Before, however, describing the next part of process, we should notice that a worm-tub ci, supplied with water from a service-pipe, is placed on the top of the decomposing vessel ; the vapours from the boiling tsqntal beneath enter this worm, and are therein condensed by transmitting their caloric to the surrounding water ; and the water thus made hot, serves for replenishing the vat a with fresh portions from time to time, as it may be re quired, by means of a connecting tubeffurnished with a stop-cock. The conten'e
of the vessel b, after decomposition, are discharged into the saturating vessel', and, during the time that it is running, a quantity of lime, or chalk, in solution, may be poured in among it as long as any effervescence continues, which will vary according to the degree of concentration of the acid; but, in general, three pounds of chalk, or lime, will be found sufficient to saturate each pound of sul phuric acid employed in the preceding part of the process. The liquid in the saturating vessel having now become transparent, it is to be drawn off' into the fermenting vat Is, placed beneath, leaving the precipitated sediment undisturbed at the bottom while the clear liquor is running. The discharge cock being closed, the sediment may be atirred up with a quantity of water, to take up whatever saccharine or fermentable matter it may contain ; this should be allowed to subside again, and the clear liquor then to be added to the former in the vat beneath. To promote the fermentation, a quantity of yeast is now to be added to the liquid, in the proportion of three pounds to every hundred pounds of potatoe pulp. During the fermentation, which usually occupies from fifteen to twenty days, the temperature of the liquid should be preserved at from 90° to 100° Fahr., and the atmosphere of the room where it is conducted, at from 80° to 85°. The patentee having discovered that the introduction of hydrogen gas facilitates the fermentative process, besides increasing and improving the product, further directs that the vat should be furnished with a tube i, along which the gas is to be forced, by means of a pump, into the liquid. The tube, after descending to the bottom of the vessel, takes a hori zontal serpentine course ; in this part it is perforated with numerous small holes, through which the gas escapee and bubbles up through the liquid. This injection of the gas should be continued until the carbonic acid gas, in the upper part of the vat, contains an excess of the hydrogen. The patentee is of opinion that the introduction of hydrogen gas may be very advantageously used, not only in this process, but in the fermentation of all matters from which spirit or alcohol is to be extracted. When the vinous fermentation has ceased, the liquor is to be drawn off through the tube into the still k. This still is of the ordinary construction, except that instead of having a large head, or capital, it has a long neck rising perpendicularly from the body, the object of which is, that the aqueous part of the vapours may be condensed before entering the inclined part, and fall back into the still, while the more volatile or spirituous pass on alone into the bent arm, and from thence into the refri gerator or worm-tub 1, where it is converted into the ordinary first product of dis tillation, called low wines (which is a very weak spirit). The low wines are then taken to another called the low wine-still, a section of which is 'hewn in the accompanying engraving.