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But lately fume veflels made of liich unannealed glafs haVe been difcovered, which have the remarkable property of re- fitting very hard ftrokes given from without, though they fhiver to pieces by the fhocks received from the fall of very light and minute bodies dropped into their cavities. Thofe glajfes may be made of any fhape ; all that needs be ob- ferved in making them, is to take care that their bottoms may be thicker than their fides. The thicker the bottom is, the eafier do the glajfes break. One whofe bottom was three fingers breadth in thicknefs, flies with as much eafe at leaft as the thinneft glafs. Some of thefe veflels have been tried with ftrokes of a mallet, fuffidcnt to drive a nail into wood tolerably hard, and have held good without breaking. They alfo refitt the fhock of feveral heavy bodies let fall into their cavities, from the height of two or three feet. For inftancc, mufket balls, pieces of iron, or other me- tal : pyrites, jafper, wood, bone, &c. but this is not fur- prifing, as other glajfes of the fame iize do the fame. -But, the wonder is, that taking a fhiver of flint of the fize of a fmall pea, and letting it fall into the glafs only from the height of three inches, in about two feconds the glafs flies, and fornetimes the very moment of the fhock : nay, a bit of flint no larger than a grain dropt into feveral glajfes fuc- ceflively, though it did not immediately break them, yet they all flew, being fet by, in Iefs than three quarters of an hour. Phil. Tranf. ibid. p. 509.
Some other bodies produce a like effect with flint : for in- ftance, fapphire, porcelain, diamonds, hard tempered tteel, as alfo marbles, fuch as boys play with ', to which add pearls from the animal kingdom k .[ — ' Phil. Tranf. ibid, p. 510. feq. h tbid. p. 512.-^]
The experiments fucceeded alfo when the glajfes were held in the hand, retted on a pillow, put in water, or filled with water. It is alfo remarkable, that the glajfes broke, upon their bottoms being flight] y rubbed with the finger, though fomeof them did not fly till half an hour after the rub bin"-. If the glajfes be every where extremely thin they do hot break in thefe circumf lances.
Some have pretended to account for thefe phenomena, by faying, that the bodies dropped into thefe veflels caufe a concuflion, that is ttronger than the coheflon of the parts of the glafs, and that confequently a rupture of the fame mutt enfue. But, why does not a ball of gold, filver, iron, cop- per, or feveral other bodies, even a thoufand times heavier than a fhiver of flint, equally caufe this concuflion, and break the glajfes ? Is it becaufe they are not elaftick ? But furely iron is more fo than the end of one's finger K [ — ' Ibid. p. 513. and fee p. 514, 515. the experiments of this kind made before the Royal Society.]
Mr. Euler has endeavoured to account for thefe appearances from his principles of percuflion. He thinks this experi- ment entirely overthrows the opinion of thofe who mea- sure the force of percuflion by the vis viva d , and he thinks the principles he has eftablifhed c , give a clear folu- tion of this phenomenon. According to thefe princi- ples, the extreme hardnefs of the flint, and alfo its an- gular figure, which makes the fpace of contact with the glafs veflel extremely fmall, ought to caufe an impreflion on the glafs, vaftly greater than lead or any other metal f ; and this may account for the flint's breaking the veflel, though the bullet, even falling from a confiderable height, does no damage. — [ c Mem. Acad. Berlin. 1745. p. 47. d See
Force. e Mem. Acad. Berlin. 1745. p. ii,fq. { See Force,]
Hollow cups made of the green bottle glafs, fome of them three inches thick at bottom were inflantly broken, by a Oliver of flint weighing about two grains, though they had refilled the fhock of a mufket ball from the height of three Feet. Phil. Tranf. Ibid. p. 515.
Colouring ef Glass. That the colours given to glafs may have their full beauty, it mutt be obferved, that every pot when new, and firft ufed, leaves a foulnefs in the glafs. from its own earthy particles ; fb that a coloured glafs made in a new pot can never be bright, or perfectly fine. For this reafon, the larger of thefe when new may be glazed with white glafs, but the lecond time of ufing the pots lofe this foulnefs. Thofe pots which have ferved for one colour mufl not be ufed for another, for the remainder of the old matter will fpoil the colour of the new. The colours muft be very carefully calcined to a proper degree, for if either too much or too little they never do well ; the proper proportion, as to quantity, muft alfo carefully be regarded, and the furnaces muft be fed with dry, hard wood. And all the procefles fuc- cecd much the better if the colour be ufed dividedly, that is a part of it in the fritt, and the reft in the melted me- tal. Nen's Art of Glafs, p. 44.
Balas coloured Glass is made thus : put into a pot cryftal fritt thrice warned in water; tinge this with manganefe prepared into a clear purple ; to this add alumen cativum lifted fine, in fmall quantities, and at feveral times : this will make the glafs grow yellowifh, and a little redifh, but not blackifh, and always diffipates the manganefe. The laft time you add manganefe give no more of the alumen cativum, wnlefs the colour be too full. Thus will the glafs be exactly Suppl., Vol. I*
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of the colour of the balas ruby. Ntrf* Art of Glafs, p. 183., RedGhAss. A blood ted glafs may be made in the following manner: put fix pound of glafs of lead, and ten pound of common glafs into a pot glazed with white glafs ; when the whole is boiled and refined, add by fmall quantities, and at fmall diftances of time, copper calcined to a rednefs, as much as on repeated proofs is found fufficient ; then add tartar in powder by fmall quantities at a time, till the glafs is become as red as blood ; and continue adding one or other of the ingredients till the colour is quite perfect. Ibid. p. 182. Yellow Glass. It is a neceftary remark in glafs making, that the cryftal glafs made with fait, that has an admixture of tartar, will never receive the true gold yellow, though it will all other colours ; for yellow glafs, therefore, a fait muft be prepared from polverine or pot-afhes alone to make the glafs. Ner?$ Art of Glafs, p. 1 2. Glass of Antimony may be deprived of its emetic quality, by digefting it with pure fpirit of vinegar till the menftruum be highly tinged. Boyle's Works Abr. Vol. I. p. 74. Where he fays, that if you abftract this liquor, and digeft good rec- tified fpirit of wine on the remaining powder, an excellent tincture againft feveral difeafes may be obtained. Gl Ass-Cbakedony. A mixture of feveral ingredients, with the common matter of glafs, will make it rcprefent the ferrii- opake gems, thejafpers, agates, chalcedonies, &c. The way of making thefe feems to be the fame thing with the method of making marbled paper, by feveral colours dif- folved in feveral liquors, which are fuch as will not readily mix with one another when put into water, before they are caft upon the paper which is to be coloured. There are; feveral ways of making thefe varioufly coloured glajfes, but the beft is this : diflblve four, ounces of fine leaf filver in a glafs veflel in ftrong aqua fortis, flop up the veflel, and fet it afide.
In another veflel diflblve five ounces of quickfilvcr in a pound of aqua fortis, and fet this afide.
In another glafs veflel diflblve in a pound of aqua fortis three ounces of fine filver, firft calcined in this manner : amal- gamate the filver with mercury, mix the amalgama with twice its weight of common fait well purified, put the mix- ture in an open fire in a crucible, that the mercury may fly off, and the filver be left in form of powder. Mix this powder with an equal quantity of common fait well purified^ and calcine this for fix hours in a ftrong fire j when cold, wafb off the fait by repeated boilings in common water, and then put the filver into the aqua fortis. Set this folutibri alfo afide. Neri'fi Art of Glafs, p. 79. In another veflel diflblve in a pound of aqua fortis three ounces of fal armoniac, pour off the folution, and diflblve in it a quarter of an ounce of gold. Set this alfo afide. In another veflel diflblve three ounces of fal armoniac in a pound of aquafortis, then put into the folution, cinnabar, crocus martis, ultramarine, and ferretto of Spain, of each half an ounce. Set this alio afide.
In another veflel diflblve in a pound of aqua fortis three ounces of fal armoniac, then put into it crocus martis made with vinegar, calcined tin, zafFer, and cinnabar, of each half an ounce ; let each of thefe be powdered very fine, and put gently into the aqua fortis. Set this alfo afide. Neri', p. 80. In another veflel diflblve three ounces of fal armoniac in a pound of aqua fortis, and add to it brafs calcined with brim- ftone, brafs thrice calcined, manganefe, and fcales of iron which fall from the fmith*s anvil, of each half ah ounce ; let each be well powdered, and put gently into the veflel. Then fet this alfo afide.
In another veflel diflblve two ounces of fal armoniac in a pound of aqua fortis, and put to it verdigreafe an ounce^ red lead, crude antimony, and the caput mort-uum of vitriol, of each half an ounce ; put thefe well powdered leifurely into theveflel, and fet this alfo afide. Neri, p. 81. In another veflel diflblve two ounces of fal armoniac in a pound of aqua fortis, and add orpiment, white arfenic, painters lake, of each half an ounce : keep thefe nine vef- fels in a moderate heat lor fifteen days, fhaking them well at times. After this pour all the matters from thefe veflels into one large veflel, well luted at its bottom; let this ftand fix days, fhaking it at times, and then fet it in a very gentle heat, and evaporate all the liquor, and there will remain a powder of a purplifh green. Ibid. p. 82. When this is to be wrought, put into a pot very clear metal, made of broken cryftalline and white glafs, that has been ufed ; for with the virgin fritt, or fuch as has never been wrought, the chalcedony can never be made, as the co- lours do not flick to it, but are confirmed by the fritt. To every pot of twenty pound of this metal put two or three ounces of this powder at three feveral times; incorporate the powder well with the glafs, and let it remain an hour be- tween each time of putting in the powders. After all is in, let it ftand twenty-four hours ; then let the glafs be well mixed, and take an e.tTay of it, which will be found of a yellowifti blue ; return this many times into the furnace ; when it begins to grow cold, it will fhew many waves of different colours very beautifully. Then take tartar eight ounces, foot of the chimney two ounces, crocus martis made with 12 I brimn
