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7 Rough Eflex potath, the very best
51 He also mentions that the average price of barilla, for three years paft, was twenty-seven pounds ten shillings per ton.
We fear, that unless the Bombay alkali could be afforded at a lower rate than Mr. Scott mentions, it has little chance of becoming an article of commerce to this country.
We have heard of a kind of soap that is manufactured in India, which may be employed in walbing with sea water, with the same effect as common soap has with good soft water. It would be a matter of some importance to a maritime and commercial nation to have the nature of this composition ascertained.
POLITE ARTS. Mr. William Yates, surveyor, having, at his own expence, made a new survey of the county of Lancafter, and presented a copy of it, with an atteftation of its accuracy by a considerable number of the inhabitants of that county, obtained the Society's premium.
MANUFACTURES. Under this head, Mr. Thomas Greaves, near Warrington, transmits to the Society some specimens of paper made from the bark of withens, i. e. willow twigs. The bark was stripped from the twigs in autumn, which must have been attended, we should think, with a considerable expence. Had they been pulled off in the month of April, just after the sap begins to flow, as is commonly done by those who carry on the business of fine basket-making to a great extent, it could have been done at a much smaller charge. As great quantities of this bark are thrown away as entirely useless, it would seem that it might furnish materials for a considerable quantity of paper, at a very low price. For Mr. Greaves has proved experimentally, that it can be easily converted into paper without any addition—and that it is by no means necessary it should either be previously dried, or freed from its leaves, before it be applied to that use. should think hop-binds would answer this purpose ftill better.
We have here some farther atteftations of the goodness of Englih-made paper for the purpose of taking impressions from copper plates, so that, it is probable, this branch of manufacture will soon be fully established in Great Britain.
As it appears probable that the breeding of filk worms may in time be introduced into this country, the Society beftow a due degree of regard to every observation that may tend to give useful information on this point. In the present volume, the public are favoured with an intelligent letter on that subject from Mr. Peter Noaille, of Greatness, Kent. It relates to the proper
mode of winding off filk from the cocoons. It states, that if a thread be formed of 18 or 20 cocoons, the value of such filk may be estimated at 20 shillings per pound, of 16 ounces, while a pound of filk composed of the very fame materials, consisting of only fix or eight cocoons, would be worth 30 hilo lings, and if four or five cocoons only, it might vie with the moft superlative produce of Italy, that would be worth 40 fillings per pound. He then estimates the expence at which this superior sort may be obtained. With this view, he states that one woman and a girl can easily wind off one pound of filk, of the fineft quality, in a day; and that the same woman and girl could wind, of the coarseft sort of filk, fix, eight, or more (lay ten) pounds in a day. Let the wages of the woman and her girl be stated at one thilling per day.
The cost of winding 10 pounds of filk of the finest fort, would therefore be The price of it at 40 shillings per pound
19 100 The cost of winding 10 pounds of the coarseft sort would be
O I O The price of it at 20 Thillings per pound
0 0 Net price
So that the profit by winding it off fine would be 9 II
II 0 An attempt had been made to spin the filk dire&tly from the cocoons, without having been previously reeled, which he lhews to be, in all circumstances, a very un-ceconomical practice.
MECHANICS. Under this head, we find a description of a new machine for measuring angles, invented by Mr. Matthew Hill, of Scarborough.— A sector, and tool for setting wheels and pinions in watch work, invented by Mr. Joseph Ridley.-And a carriage for conveying timber over soft or boggy land, by Mr. Joha Besant, Westminster; of none of which can we convey an accurate idea, without the plates.
The volume concludes with the usual lists of rewards befowed-presents received – premiums proposed, and the preLent members of the Society.
Art. ART. V. Experiments and Observations on Animal Heat, and the Inflammation of combustible Bodies : Being an Attempt to resolve the Phenomena into a general Law of Nature. By A. Crawford, M. D. F. R. S. L. & E. and Member of the Philosophical Socie. ties of Dublin and Philadelphia. The Second Edition, with very large Additions. '8vo. 75. Boards. Johnson. 1788. HE theory of animal heat and combuftion, as delivered by Dr.
work, is now more fully established by the results of many new experiments which appear to have been made, with the moft scrupulous attention to accuracy, in order to ascertain some new facts, and to correet some mistakes in the conclusions drawn from those that were before presented to the public.
It seems now to be the prevalent opinion, that experiments, and inductions from shem, are the only means .by which we are permitted to interpret the characters impressed by the Deity on his works; and the pbilosopber, who is thus employed in cultivating natural knowlege, is well aware that this method of searching after truth, necefsarily demands much labour, and patient investigation, aided by fagacity, and directed with judgment.
Dr. Crawford pleads, in excuse for the late appearance of this second edition (containing new discoveries, and the correction of errors), the dishculty in pursuing, and the time requifite for making, experimental researches. He is convinced, as indeed every true philosopher muft be, that to correct errors is the beft method of apologizing for them; and that though the free communication of discoveries is effential to the progress of knowlege, yet it is of much greater importance to the interests of science, that facts should be well ascertained, than that they should be speedily published. He does not, however, mean to infinuate that the facts which he has now submitted to the public are free from error; miftakes may easily arise in every attempt, where so much nicety is required, to determine the reJations between the subtle elements of fire and air; and he hopes, that such of them as may be found in his work, will, by the candid public, be ascribed to the imperfections of our senses, or the instruments employed in the course of the experiments.
The abftrufeness of the subject, and the novelty of Dr. Crawford's theory*, were probably the reasons why his doctrine met with some opposition, on its firft appearance; especially by Mr. Morgan t, who made many pertinent reflections on Dr. Crawford's opinions. As an amicable contention, such as Mr. Morgan's with Dr. Crawford really was, always promotes science,
# For an abridgment of which see Rev. vol. lxi. p. 378.
we hoped that the Do&or would be incited to repeat, diverfify, and extend bis experiments. This he hath now done, and his theory, not materially altered, has received much additional support.
As we have before given an abstract of our ingenious Au. thor's theory of animal beat, and of tbe inflammation of combuftible bodies, it is unnecessary that we should repeat it. We thall therefore only endeavour to refrelh the memory of our readers, by informing them that according to the results of Dr. Crawford's experiments, it appears that pure air, containing a large portion of elementary fire, is, by inspiration, received into the lungs; and that the blood, impregnated with phlogiston, is re. turned from the extremities. Now the attraction of air to pblogiston being greater than that of blood, the phlogiston quits the blood, and unites with the air ; the air at the same time depositing part of its elementary fire: and the capacity of the blood for receiving heat being increased by the change it undergoes in lofing its phlogiston, the elementary fire before deposited by the air will be absorbed by the blood. The blood in its passage through the capillaries is again impregDated with phlogiston, in consequence of which, its capacity for heat is diminithed, and therefore, in the course of the circulation, it will give out, and diffuse over the whole system, the heat acquired in the lungs: or, in a word, in respiration, the blood is continually discharging phlogiston, and absorbing heat, and on the contrary, during its circulation, it is continually imbibing phlogiston, and emitting heat.
With respect to the inflammation of combustible bodies, it appears, by Dr. Crawford's experiments, that when atmospherical air is converted into fixed air and aqueous vapour, a great part of its heat is detached: it appears also that the capacities of bodies for containing heat are increased by parting with their phlogiston in the process of combustion. Hence in the act of inflammation, the phlogiston that is separated from the inflammable body unites with the pure air, which, at the same time, being converted into fixed air, and aqueous vapour, gives off a large portion of its abfolute beat; this absolute beat, thus extricated, produces an intense degree of fenfible bear, and if the extrication be sudden, the heat will burft forth into flame.
The explanation which this theory affords to the several pheDomena attendant on animal heat, and combustion, is a Atrong confirmation of its truth, independently of the easy solution which it gives of a great variety of facts. The physiologist will here find some of those parts of the animal economy explained which bisherco have been unaccounted for; the natural philosopher and chemift will also find many facts elucidated which could scarcely be solved, on any other hypothesis.
With respe&t to the nature of heat, whether it be a substance or a quality, our Author's doctrine is totally unconnected with any hypothesis concerning it, being founded on this fimple fa&t deduced from experiment, viz. that the changes wbich are produced in the temperatures of different bodies by the application of given quantities of heat, are different. He bas, indeed, in many places, used expressions which seem to favour the 'materiality of heat; but his role motive for adopting such language was, as he says, because it appeared more consonant to the facts which he had established by experiment. He is nevertheless perfuaded that it will be extremely difficult to reconcile many phenomena with the supposition that heat is a quality. It is not easy to comprehend on this hypothefis, bow heat can be absorbed in the processes of fusion, evaporation, or combustion ; or how the quantity of heat in the air can be dimin hed, and that in the i blood increased, by respiration : but the opinion that heat is a diftinct substance, or an element sui generis, being adopted, the phenomena admit an easy and opvious interpretation. Fire, the Doctor thinks, will, on this fuppofition, be considered as a principle which is distributed in various proportions throughout the different kingdoms of nature; be supposes the mode of its union with bodies, to resemble that particular species of chemical union, wherein the elements are combined by the joint forces of pressure and attraction, such as the combination of fixed air with water. If, however, fire be a substance, subject to the laws of attraction, the mode of its union with bodies seems to be different from that which takes place in chemical combinations; for in these, the elements, as Dr. Crawford observes, acquire new properties, and lose those by which they were characterized before the union : but he has thewn that fire does not, in consequence of its union with bodies, lose its diftiriguilhing properties; consequently, we have no direct proof of its materiality. Dr. Crawford's conclusions are, however, as we hinted above, not in the least affected by the nature of heat or fire; they are simply the facts resulting from experiments and the testimony of the lenses, and they must be admitted notwithstanding any adopted hypothesis. The subject is, double Jess, extremely intricate ; and much time, a long series of accurate experiments, and the most minute observations, are perhaps still requisite to complete the investigation of the nature of this subtle principle. Few years, indeed, have elapsed, fince philosophers have turned their attention, in a proper manner, to the subject; and from the progress that is already made, we may hope that a few more years will unfold what is now wrapt in abscurity, or involved in error.