[126] PROCESS of Converting the SMOKE of STEAM-ENGINES into TAR. fupplied with coal kept burning at "In this procefs the fmoke is de- "The procefs requires but little attendance, the principal labour being that of fupplying the fuel. In any one of the tar works the quantity of coal ufed is about twenty tons per day; three labourers, with a foreman, are fufficient for the whole bufinefs: the quantity of tar produced will be about twenty-eight barrels, of two hundred weight and an half, in fix days, worth ten fhillings per hundred, or twenty-one barrels of pitch, of the fame weight, worth fifteen fhillings per hundred; though I was affured, upon the spot, by a very intelligent perfon, that fome coal is of fo bituminous a quality, as to give one eighth its weight, of tar: but the quantity above stated is about the average produce. "In order to bring the above practice within the fociety's inten tions, an alteration in the erection of fteam-engines, furnaces, &c. muft take place; the alteration will be no more than that of erecting them be. low ground, instead of above: and when raifing water is the main ob. ject, an adoption of the forcing or lifting pump inftead of the fucking pump, or the fucking pump may be ftill employed, wherever the fall of ground gives an opportunity of letting off the water raifed, by an aqueduct; in which cafe, the lift being shortened, and lefs power neceflary, ample amends will be thereby made for the expence of such aqueduct. "Such kind of buildings, from a low fituation, within the earth's furface, will certainly acquire additional ftability: and to thofe who are acquainted with the trifling expence of removing foil to only fmall distances, the additional charge will appear trifling, and will be more than recompenfed by fuch acquired ftability. In fome local fituations, in hilly countries, the smoking works being erected at the foot, and the tar-funnel higher up the hill, a communication may be effected without fuch alteration. Perhaps it may be right for the fociety to offer a premium to the first person who fhall erect a steam engine, or other fimilar work, upon this plan. "To prove the above idea is not ill-founded, I beg leave to report, that about three weeks ago, I particularly examined the tar work on Dudley wood; and found the foreman of the work intelligent and communicative; and walking with him on the top of the tar-funnel, obferved a prodigious smoke arife from a fteam-engine, about thirty yards yards diftant, fresh fuel having juft been added. When I put this queftion, would that smoke make tar, if it paffed into your funnel? he anfwered, moft certainly. Would your confining it there, prevent the fire burning below, fufficient to do its office of working the fteam-engines? anfwer, certainly not; as our fmall funnels allow fufficient draught to keep the fire burning, which draught we can increase or diminish at pleafure. I find by reports from other quarters, that fuccefsful attempts have been made to make cokes of the coal employed in working fteamengines the additional improve ment of making tar from the smoke, would not only prevent annorance to the neighbourhood, but alfo apply to the beft advantage every particle of that valuable and comfortable article, coal; prodigious quantities of which are at prefent wafted by being burned in one place for heat only, in another for cokes only; when, by due attention, both purpofes may in many cafes be effected at the fame time. "I was informed upon the fpot, from undoubted authority, that the confumption of coal in Mr. Wilkin fon's great works, at Bradley, is one hundred tons per day: about one fifth of the fmoke is actually employed in making of tar; and the remainder, or the fmoke of eighty tons per day, flies away. This, if collected, would yield upwards of eighteen barrels of tar, of two hundred and an half each: and if the fmoke of the great works of the kingdom was in general collected for the fame ufe, what a prodigious addition would it be, to the produc tion of a commercial and neceffary article, which always finds a ready market, and will in many inftances fupply the place of the vegetable tar, at prefent imported from abroad! "That fome idea may be formed of the confumption of coal in steam. engines for raifing water, I beg leave to report the following, of which I had certain information upon the fpot; namely, that fome fuch engines individually confume one hundred tons per week of coal; that others, though powerful, with the improvements of Meffrs. Boulton and Watt, are kept on with about twenty-five tons per week; and that the weekly confumption varies between thofe two quantities, viz. from twenty-five to one hundred tons." CONJECTURES refpecting the FORMATION of NITRE. [From the third Volume of Townsend's Journey through Spain, in the years 1786 and 1787.] and towards noon become white round the edges; this they collect, and find that land, on which has been laid much dung, is the most productive. Once collected, it will endure for ages; and, having been expofed to the influence of the fun, and of the air, yields the fame quan tity as at firft on every fubfequent filtration. In the places where they find this earth, there is neither lime tone, chalk, nor gypfum; and afhes being extremely fcarce, none are used at the bottom of the fil ters. "I have already confidered this wonderful production as a merchant; and happy fhould I be, were I qualified to difcufs it with any fatisfaction as a chemist. "Here a thoufand queftions crowd in upon the mind. From whence does this earth colle& the vegetable alkali, whence the nitrous acid? fuppofing the former to be originally the refult of putrefaction, yet, after the earth has been lixiviated, and all the vegetable alkali has been carried off by water, how is it impregnated afresh, merely by expofure to the fun and air; and where does it obtain this inexhaustible supply both of the alkali and its combining acid? but, if we reflect, that, with the nitrous falt, there is conftantly found muria, or fea-falt, in confiderable quantities; whence does it derive the fodil alkali, and whence the muriatic acid, not once, but upon every fubfequent expofure? "It is well known that old mortar produces fix kinds of falt: for, befide the two juft mentioned, both the nitrous and the muriatic acid. are found combined with magnefia and with calcareous earth. But, if we recollect, at Anover and Aranjuez we faw Epfom and Glauber's falt, with the muria and the nitre, and both those falts contain vitriolic acid. "Here, then, new questions will arife. What is the relation betweenthefe various fubftances, of chalk, magnesia, the fofil, and the vegetable alkalis? what connection can we trace between the muriatic, nitrous, and vitriolic acids? and, is there one common principle of acidity? "This question will be both more natural and more interefting, when we confider, as far as relates to England, France, and Spain, the only countries which have come under my obfervation, that, in proportion to the quantity of fun, the chalk is found impregnated with vitriolic acid, and forms felenite or gypfum. At least it may be obferved, that in our island, we have much chalk, and little gypfum; that in France both thefe fubftances abound; whilft in Spain, there is very little chalk, and a profufion of gypfum, more efpecially in Arragon, and in the fouthern provinces. Indeed a learned naturalift, who refided many years in Spain, and traversed it in all directions, with a view to minerals, aflures us, that he had never difcovered there the least veftige of chalk. (v. Bowles, p. 13.) But I have already noticed it in one place; and in the neighbourhood of Granada it is likewife found, although I was not able to identify the spot. "His obfervation is however ingenious, and worthy of attention. He never met with it; I saw it only at Cervera, here, and at Picacente. "The connection between chalk and gypfum became evident to me from the moment that I difcovered flinty gravel in the latter, precifely fuch as we always meet with in the former. Hence it feems to be plain, either that chalk was gypfum, and has loft its vitriolic acid, or that gypfum was once chalk, and has made this acquifition. I am inclined to adopt the latter hypothefis: and, if this be the true one, we must inquire whence has it derived the acid? was the chalk impregnated with the vitriolic acid, whilft it remained covered by the waters of the ocean? or is the acquifition fubfequent to that grand revolution to which I have frequently referred? Should we fuppofe the latter, and fhould we be inclined to feek the principle of acidity in the folar ray, we may perhaps be confirmed in this idea by the confideration, that, by means of green vegetables and water expofed to its meridian influence, all modern chemifts have produced vital, that is, dephlogisticated air, in great abundance, always in proportion to the quantity of light, or, in other words, to the greater or leffer influence of the folar rays: and that faltpetre, by diftillation, produces the fame kind of air, in the proportion of twelve thousand inches to a pound, leaving behind the vegetable alkali uncombined with acid. "Should we be inclined to grant, agreeable to the experiments of Dr. Ingenhoufz, that vegetables by day emit vital, and by night mephitic air; confidering that Mr. Cavendish produced nitrous acid by the combination of vital air with atmospheric mephitis, in the proportion of feven to three, we fhould not be at a lofs for a never-failing fource, from whence this acid may arise. "Thefe fpeculations might be purfued, and, obferving that one pound of nitrous acid, diftilled on mercury, yields one thousand eight hundred and eight cubic inches of nitrous, and one thousand niue hundred and four of vital air, we should be confirmed in our opinion that we have discovered the origin of the fought-for acid. "Nitrous air is obtained from animal fubftances fimply by putrefaction, or it may be had by the combination of inflammable and vital air: for, as Dr. Priestley has remarked, in the Philofophical Tranfactions of the 27th of November, 1788, "When either inflammable or de"phlogifticated air is extracted from "any fubftance in contact with the "other kind of air, so that the one is made to unite with the other in "what may be called its nafcent "ftate; the refult will be fixed air; "but, if both of them be completely "formed before their union, the refult will be nitrous air." "Thus, in the various facts and obfervations above related, we may fee the intimate relation and connection between inflammable, fixed or mephitic, and nitrous air; that the two latter refult from the combination of the former with vital air in given quantities; whilft, with a greater proportion of vital air, we obtain nitrous acid; and that, of these its constituent principles, in warm climates, animal fubftances are, by their putrefaction, constantly producing one, whilst vegetables, by day, are as conftantly pouring forth the other." 1791. NATURAL "I NATURAL HISTORY of the GRANA KERMES. [From the fame Volume.] HAD here an opportunity to examine the natural history of the grana kermes. It is found on the cafcoja, or quercus coccifera of Linnæus, here growing to the height of from twelve inches to two feet. The grana appear on the stems or small branches, fome near the bottom of the plant, but moftly on the upper branches, yet always protected by the leaves, and fixed to the ftem by a gluten, which both to the fight and to the touch refembles thin white leather, fpread over the ftem, and covering, like the cup or calix of the acorn, a fegment of the grana. Upon a more minute investigation, I traced the agglutinating coat through a fmall foramen into the grana, from whence it had proceed ed, and where it fpread, like the placenta, on the internal furface. "The grana were of various fizes, from an eighth to a quarter of an inch in diameter, perfectly fpherical, and covered with a white powder, which being rubbed off, the furface appeared red, fmooth, and polished. Upon the fame ftem I found the grana in three ftages. In the first I difcovered only tough membranes filled with a red juice refembling blond, but on paper leaving a ftain as bright and beautiful as the best carmine. In the fecond ftage there appeared, under the fift coat or pellicle, a thin tough membrane inclofing the eggs, now most minute, and fcarcely to be diftinguifhed without the affiftance of a convex lens. Between this membrane and the pellicle was the fame red liquor, but lefs in quantity than was contained in the former ftage. By a careful diffection I took off the pellicle which was evidently feparated from the inner membrane by what feemed to be the vifcera and The interior membrane is thin, "It is clear to me that the graną derives no kind of nourishment from the plant on which it is fixed; and from its pofition I am inclined to think, that the little animal choofes the quercus coccifera, which in its prickly leaf refembles the holly, only for the fake of fhelter and protection from birds. "I put fome of the grana into a coffee cup on the thirty-firft of May, and, June the twelfth, I discovered a multitude of animalculæ, of a bright red colour, exceedingly mi nute, running about the cup with aftonishing rapidity, but for short intervals. A friend put fomne grana into a fnuff-box, where he foon for got them; but when, at the distance of a few weeks, he had occafion to refume his box, he found the top co vered internally with dew, and a multitude of winged infects, all dead, adhering to it. "Before my excurfion to Buzot, fome peafans of Las Aguas had fpread themfelves on the adjacent mountains, where they collected more than four arrobas, or one hundred weight of grana, which they had fold in Alicant for fifteen reals, or about three hillings a pound." AC. |