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TEMPERATl'RE/or Plants, in Gardening, thf ftate of heat 

 ill which it is necciTary to keep particular forts of them, in 

 order to their ftriking or taking root, their healthy growth, 

 and their fucceeding in the beS and moft proper manner. 

 The ftate or degrees of heat, or the temperature, in all fuch 

 cafes, mull be regulated and direftcd by the nature of the 

 plants, their culture, and the fituations in which they are 

 grown. For thofe in hot-houfcs and floves, the tempera- 

 ture, in thofe of the dry ftovc kind, fliould moftly be from 

 about fifty to fevcnty degrees, according to the natures, 

 habits, and miuincrs of growth of the plants ; and in thofe 

 of the moill (love kind, from about fixty to ninety degrees, 

 as the nature of the beds and plants may be. Plants in con- 

 fcrvatorics are kept at various temperatures between thofe 

 of the firil kind of the above ftoves and that of the common 

 open air. And in greenhoufes, nearly fimilar temperatures 

 are conftantly to be preferved, in order to the raifing, and 

 to the growth of fuch plants, in the mod fuitable and beil 

 manner. 



It ii always of great utility and importance to keep the 

 temperatures as fteady as poffible, whatever its ftate may be, 

 in the growth of all thefe forts of tender plants. 



The temperatures, or ftates of heat for particular plants, 

 are moftly given under their proper heads, in defcribing 

 their culture. 



Tempekature of Milk for Cheefe, in Rural Economy, the 

 degree of heat which is the moft proper in milk for the 

 purpofe of making cheefe. From fome experiments which 

 have been lately made upon the fubjeft, this temperature 

 would fecm to be about the middle point between that of 

 fummer and blood heat ; or, perhaps, fomewhere about 

 ninety degrees of Fahrenheit's fcale may give the average 

 degree of warmth which is moft proper and neceffary in the 

 bufinefs. 



TEMPERING, in the Mechanic Jrts, the preparing of 

 fteel and iron, fo as to render them more compaft, hard, 

 and firm ; or even more foft and pliant ; according to their 

 refpeftive occafions. 



Thefe metals are tempered by plunging them, while red- 

 liot, into fome liquor prepared for the occafion : fometimes 

 pure water is ufed for that purpofe : our lockfmiths, &c. 

 fcarcely ufe any other. 



When an inftrument has been properly hardened, it is ne- 

 ceffary to give it a certain degree of foftnefs, in order to 

 adapt it for the purpofe to which it is to be applied. With 

 this view, it fliould be heated again to a certain point, 

 ufually determined by its colour, and then inftantly plunged 

 into cold water. This is called " letting it down to the 

 proper temper." It has been a queftion of difficult folu- 

 tion, how the water afts in hardening iron and fteel. It 

 is well known, fays Mr. Parkes, in his " Chemical Eflays," 

 (vol. iv. ), that the hotter any piece of iron is made, and the 

 more quickly it is cooled, the harder it will become in its 

 texture ; and he fuggefts that this may be owing to the lofs 

 of its latent heat. In confirmation of this conjeifture he 

 alleges, that iron and fteel are generally allowed to owe their 

 malleability to their latent heat. 



A compofition of divers juices, liquors, &c. has fome- 

 times been ufed ; which is various according to the opinion 

 and experience of the workman : as vinegar, moufe-ear water, 

 nettle or Spanifli radifti-water, the water oozing from broken 

 glafl"e8, fuet, fait, oil, foot, diftilled wine, fal ammoniac, 

 urine, Sec. But thefe methods are now generally abandoned. 

 Mr. Stodart, a very ingenious and fcientific cutler in Lon- 

 don, fays, (as Mr. Nicholfon informs us, Journal, vol. iv. 

 4to.) that one of his workmen makes up his charcoal fire 

 with ftiavings of leather, finding that this is effeftual in pre- 



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venting the tools from cracking in the procefs of hardening ; 

 and he fays, that he has found no advantage from the ufe of 

 fait in the water. 



To harden and temper Englidi, Flemifh, and Swedifli 

 fteel, you muft give them a pretty high heat ; then fuddenly 

 quench them in water to make them hard ; but Spanifli and 

 Venetian fteel will need only a blood-red heat before they 

 be quenched. 



In confequence of this operation, all the qualities of fteel 

 are changed ; fo that from being very duttile and foft, it 

 becomes fo hard and ftifF, that it is no longer capable of being 

 cut by the file, but is itfelf capable of cutting or piercing 

 very hard bodies, and that it does not yield to the hammer, 

 but may be fooner broken in pieces than extended. It be- 

 comes alfo fonorous, brittle, very elaftic, and capable of ac- 

 quiring the moft beautiful polifh. This hardnefs and duc- 

 tility of fteel may be divcrfified by vai-ying the temper. 

 The hotter the fteel is when tempered, and the colder the 

 water into which it is plunged, the greater hardnefs it ac- 

 quires, but at the fame time it becomes fo much more brittle. 

 The coldnefs of the water may be increafed by diflblving 

 falts in it : obfcrving that water is always colder while the 

 falts continue diflblving ; and that the fteel will cool fooner 

 by being ftirred about or placed in a ftream, fo as to come 

 in contaft with water not already made warm. On the 

 contrary, the lefs hot the fteel is when tempered, and the 

 hotter the water is in which it is tempered, the lefs hard it 

 becomes, and alfo the greater duftility it retains : and the 

 proper degree of heat is always relative to the ufe for which 

 the tools made of the fteel are intended. 



If the fteel be too hard or brittle for an edged tool, &c. 

 let it down by rubbing a piece of grindftone or vvhetftone 

 hard upon the work, to take off the black fcurf : then 

 brighten, or heat it in the fire : and as it grows hotter, you 

 will fee the colour change by degrees, in the manner and 

 by the gradations ftated under the article Cutlery. 



Saw -makers temper their tools by rubbing them over with 

 fuet or other greafe, and then heating them gradually till 

 the temperature of each tool is fufficiently raifed to fet fire 

 to the greafe of itfelf and occafion it to blaze. The}' are 

 thought to acquire in this mode of treatment a temper equal 

 to that which would be obtained by heating them in the 

 ufual way, till they became of a deep blue. This opera- 

 tion, which is praftifed at Sheffield, is called " blazing." 

 For the method of tempering files, in which the great de- 

 fideratum is to blend tenacity with hai-dnefs, fee File. 



In the year 1789, Mr. David Hartley took out a patent 

 for a method of tempering fteel by the aid of a pyrometer 

 or thermometer applied near to the furface of the article, 

 and at the fame time recommended the ufe of heated oil, in 

 which (he fays) many dozens of razors or other tools might 

 be tempered at once with the utmoft facility, and the vari- 

 ous degrees of heat necefiary for different purpofes might 

 fpeedily be determined by experiment. (See Nicholfon's 

 Journal, vol. i. 410.) An improvement of this principle 

 has been fince fuggefted by Mr. Parkes ( Chem. Efl". vol. iv. ) 

 by providing a bath of oil or of fome kind of fufible metal 

 for the tempering of every fpecies of edged tool, which 

 contrivance would, in his opinion, give to this operation a 

 greater degree of certainty, than has ever been experienced 

 by thofe who have condufted fuch manufaftories. See 

 Tilting. 



Steel is ufually fold tempered, becaufe in many manu- 

 faftures, the cuftom is to temper it as foon as it is made, 

 probably that the purchafers of it may be better able to 

 judge of its quahty. When this ileel is to be ufed, it muft 

 be untempered by heating it more or lefs, and letting it 



cool 



