am affured, however, her powers are fomewhat impaired fince her arrival here, and that she does not poffefs that compafs or extent at prefent, which he had two years ago. The character of caprice, which he maintained in the fouth ern parts of Europe, fhe has not loft here, as they univerfally afcribe this quality to her in the highest degree. She was at Milan, when the Emprefs engaged her to fing in her court. The price fhe demanded was 7000 rubles (or about 1500l. fterling) a year, befides a houfe and carriage; nor would the relax the leaft article of the fum. They remonftrated with her on the unreafonableness of fo enormous a falary; and, to induce her to diminish it, informed her, that a field-mar fhal had no more. "If that be the cafe, (faid she) I would advise her Majelty to make one of her marfhals fing." Her perfon, strictly confidered in itself, is by no means irrefiftible; he does not exceed, if fhe reaches, the middle fize; her features are fmall, and her eyes blue; but her neck is exquifitely white; and, as her drefs ufually difclofes more than can ftrictly be confined to that part of the human body, it cannot be gazed on with impunity. Her attractions have not failed to procure her many admirers during her ftay here, and the has had her favourite Mufcovite, as well as her Sicilian lover. Though her falary is fo ample, it is only on peculiar occafions and great feftivals that she usually fings." NATURAL HISTORY. The Suppofed Effect of boiling upon Water, in difpofing it to freeze more readily, afcertained by Experiments. By Jofeph Black, M. D. Profeffor of Chemistry at Edinburgh, in a Letter to Sir John Pringle, Bart. P. R. S. From the Philofophical Tranfactions. To Sir John Pringle, Bart. P. R. S. Dear Sir, W E Edinburgh, Feb. 11, 1775. calm and clear frolt; and I immediately feized the opportu nity, which I miffed before, to make fome experiments relating to the freezing of boiled water, in comparison with that of water not boiled. I ordered fome water to be boiled in the tea-kettle four hours. I then filled with it a Florentine flask, and immediately applied fnow to the flask until I cooled it to 48° of FAHRENHEIT, the temperature of fome unboiled water, which stood in my study in a bottle; then putting four ounces of boiled, and four of the unboiled water, feparately, into two equal tea-cups, I expofed them on the outfide of a north window, where a thermometer pointed to 29. The confequence was, that ice appeared firft upon the boiled water; and this, in feveral repetitions of the experiment, with the fame boiled water, fome of which were made nine hours after it was poured out of the tea-kettle. The length of time which intervened between the first appearance of ice upon the two waters was different in the different experiments. One caufe of this variety was plainly a variation of the temperature of the air, which became colder in the afternoon, and made the thermometer defcend gradually to 25°. Another cause was the difturbance of the water; turbed now and then by stirring it gently with a quill tooth-pick, the ice was formed upon it as foon, or very nearly as foon, as upon the other; and, from what I faw, I have reafon to think, that were it to be stirred inceffantly, provided at the fame time the experiment were made with quantities of water, not much larger or deeper than thefe, it would begin to freeze full as foon. In one of thefe trials, having infpected my tea-cups when they had been an hour expofed, and finding ice upon the boiled water, and none upon the other, I gently ftirred the unboiled water with my tooth-pick, and faw immediately, under my eye, fine feathers of ice formed upon its farface, which quickly increased in fize and number, until there was as inuch ice in this cup as in the other, and all of it formed in one degree without freezing; and, if they have not the means of making it colder, may continue fluid for any time, provided it be not dif turbed: the refrigerating causes of that part of the world when they have done fo much, have done their utmost, and can act no further upon the water. But this cannot happen to the boiled water; when the refrigerating caufes have cooled it to 320, the next effect they produce is to occafion in it the beginning of congelation; while the water is afterwards gradually affuming the form of ice, we know, by experience, that the temperature of it must remain at 32°; it cannot be made colder, fo long as any confiderable part of it remains unfrozen *. The refrigerating caufes continue, therefore, to have power over it, and to act upon it, and will gradually change the whole into ice, if their action be continued fufficiently long. minute of time, or two at moft. And in the rest of the trials, though the congelation began in general later in the unboiled water than in the other; when it did begin in the former, the ice quickly increased fo as, in a very short time, to equal, or nearly equal in quantity, that which had been formed more gradually in the boiled water. The opinion, therefore, which I have formed from what I have hitherto feen is, that the boiled and common water differ from one another in this refpect; that whereas the common water, when expofed in a ftate of tranquillity to air that is a few degrees colder than the freezing point, may easily be cooled to the degree of fuch air, and ftill continue perfectly fluid, provided it ftill remain undisturbed: the boiled water, on the contrary, cannot be preferved fluid in thefe circumitances; but when cooled down to the freezing point, if we attempt to make it in the leaft colder, a part of it is immediately changed into ice; after which, by the continued action of the cold air upon it, more ice is formed in it every moment, until the whole of it be gradually congealed before it can become as cold as the air that furrounds it. From this difcovery it is eafy to understand, why they find it neceffary to boil the water in India, in order to obtain ice. The utmost intenfity of the cold which they can obtain by all the means they employ, is probably not greater than 31° or 30° of Fahrenheit's thermometer. Common water, left undisturbed, will eafily defcend to this The next object of investigation may be the caufe of this difference between the boiled and the common water. In confidering this point, the following idea was fuggefted: as we know from experience, that, by disturbing common water, we haften the beginning of its congelation, or render it incapable of being cooled below 32°, without being congealed; may not the only difference between it and boiling water, when they are expofed together to a calm frofty air, confift in this circumftance: that the boiled water is neceffarily fubjected to the action of a disturbing caufe, during the whole time of its expo Common water, when cooled in a state of tranquillity to feveral degrees below the freezing point, will fuddenly rife up to it again, if disturbed in fuch a manner as to occafion in it a beginning of congelation, F 3 fure, fure, which the other is not? One effect of boiling water long is to expel the air which it naturally contains; as foon as it cools, it begins to attract and abforb air again, until it hath recovered its former quantity; but this probably requires a confiderable time. During the whole of this time, the air entering into it must occafion an agitation or disturbance in the water, which, though not fenfible to the eye, may be very effectual in preventing it to become, in the leaft, colder than the freezing point, without beginning to freeze, in confequence of which its congelation must begin immediately after it is cooled to that point. When I reflect upon this idea, I remember a fact which appears to me to fupport it ftrongly. Fahrenheit was the first perfon who difcovered that water, when preferved in tranquillity, may be cooled fome degrees below the freezing point without freezing. He made the difcovery while he was endeavouring to obtain ice from water that had been purged of its air: with this intention he had put fome water into little glass globes, and having purged it of air, by boiling and the airpump, he fuddenly fealed up the globes, and then expofed them to the frofty air. He was furprized to find the water remain unfrozen much longer than he expected, when at last he opened fome of his globes, in order to apply a thermo meter to the water, or otherwife examine what ftate it was in. The immediate confequence of the admiflion of the air was a fudden congelation which happened in the water; and in the rest of his globes a fimilar production of ice was occafioned by shaking them. The inference that may be drawn from thefe experiments of Fahrenheit's is fufficiently obvious; it appears to me to remove all doubt with regard to the above fuppofition. Before thefe experiments of Fahrenheit occurred to my memory, I had planned a few, fuggefted by the above fuppofition, that might have led to the fame conclufion; but the fhort duration of the froft, for one day only, did not give me time to put them in execution. This property, in oil and other greafy fubftances, of smoothing the furface of water, nay and of ftilling waves, has been more or lefs obferved, and even taken advantage of, in feveral diftant parts of the world, down to the prefent times. The inhabitants of St. Kilda themselves have been acquainted with it, as appears by the following paffage, in Martin's Defcription of the western inlands of Scotland: "The and extenfive knowledge in moft fciences would have more diftinguished him, had he been placed in a more confpicuous point of view, you will find that he had heard of your experiment on Derwent lake, and has thrown together what he could collect on that fubject; to which I have fubjoined one experiment from the relation of another gentleman. Extract of a Letter from the Rev. I fome time ago met with Mr. Dun, who furprized me with an account of an experiment you had tried upon the Derwent water, in, company with Sir John Pringle and Dr. Franklin. According to his reprefentation, the water, which had been in great agitation before, was inftantly calmed, upon pouring in only a very small quantity of oil, and that to fo great a diftance round the boat as feems a little incredible. I have fince had the fame accounts from others, but I fufpe&t all of a little exaggeration. Pliny mentions this property of oil, as known particularly to the divers, who made use of it in his days, in order to have a more fteady light at the bottom. The failors, I have been told, have obferved fomething of the fame kind in our days, that the water is always remarkably fmoother in the wake of a ship that hath been newly tallowed, than it is in one that is foul.-Mr. Pennant alfo mentions an obfervation of the like nature made by the fealcatchers in Scotland, Brit. Zool. vol. iv. Article Seal. When thefe animals are devouring a very oily fish, which they always do under water, the waves above are obferved to be remarkably fmooth, and by this mark the fishermen know where to look for them.Old Pliny does not ufually meet with all the credit I am inclined to think he deferves. I fhall be glad to have an authentic account of the Kefwick experiment, and if it comes up to the reprefentations that have been made of it, I fhall not much hefitate to believe the old gentleman in another more wonderful phænomenon he relates, of filling a tempeft only by throwing up a lit tle vinegar into the air. Extract of a Letter to Dr. Brownrigg, from Dr. Franklin Dear Sir, London, Nov. 7, 1773. I thank you for the remarks of your learned friend at Carlisle.-I "The fteward of Kilda, who lives in Pabbay, is accustomed, in the time of a ftorm, to tie a bundle of puddings, made of the fat of fea fowl, to the end of his cable, and lets it fail into the fea, behind the rudder. This, he fays, hinders the waves from breaking, and calms the fea; but the fcent of the greafe attracts the whales, which puts the veffel in danger." Does not the conclufion of this paffage afford an useful hint to the whalefishers? Sir Gilfred Lawfon, who ferved long in the army at Gibraltar, affures me, that the fishermen in that place are accustomed to pour a little oil on the sea, in order to till its motion, that they may be enabled to fee the oysters lying at its bottom; which are there very large, and which they take up with a proper inftrument. This Sir Gilfred had often feen there performed, and faid the fame was practifed on other parts of the Spanish coaft." |