Clofure of VeJJels. 26 r 



more convenient and proper for flopping fmail circular apertures, whofe interior furfaces 

 are fmooth enough to admit of their ufe, than common phial-corks : for a certain time at 

 lead, where the contents of the veflel are not corrofive, they fit more clofely than mod of 

 the glafs floppies which are ufed for this purpofe. Where however the area of the aperture 

 is confulerable, the porofity of cork and bladders, the necelTity of ufing veflels whofe mouths 

 are elliptical, and the unavoidable irregularities in the form of the ground glafs covers, which' 

 are befidcs of confiderable expence, are circumflances which render the folution of this pro- 

 blem lefs eafy than might be wifned. The clofenefs of texture which charafterifes me- 

 tallic fubftances feems to afford the befl means of removing thefe difficulties; and a quantity 

 of an amalgain. of tin is accordingly in fome mufeums fpread over the edges of the covers, by 

 which means the mifchief is in a good meafure prevented : but perhaps no method of elFeft- 

 ing this end is fo applicable to general purpofes, as that which confifls in the ufe of tin foil, 

 which is alfo in frequent pradice. It may be applied in two ways : a piece of bladder, foaked 

 in warm water, having been flretched tightly over the mouth of the jar, and tied, a piece of 

 the thickefl tinfoil, previoufly examined by interpofing it between the eye and the fun, in 

 order to dete£l the fniall fiflures which are frequently found in it, is to be laid fmoothly over 

 It with the palm of the hand, without ftretching, and, that being alfo tied, a fecond piece of 

 bladder again flretched over it : or, where the vefTel may require to be fometimesopened, 

 the foil may be laid fmoothly over the furface of a bung, and, a piece of bladder being flretched 

 over it, the whole applied in the ufual way. 



The following feems to be another efFeftual method of clofing a jar :— Let a b (Plate XII. 

 Fig. I.) be a feftion of its mouth ; c d, that of a circular rim of tin. A, an inch high, whofe 

 internal diameter is half an inch larger than the exterior diameter of the mouth of the vefTe! ; 

 ef, that of a common tin cover, B, whofe diameter is a quarter of an inch lefs than that 

 of the tin rim, A. The rim being cemented round the neck of the jar with fealing-wax, or 

 the common eleclrical cement, and the interval between it and the neck filled to the depth 

 of two-tenths or a quarter of an inch, with olive-oil*, it is clear, that if the jar be placed 

 horizontally, and the cover B put on, it becomes hermetically fealed, except in the event of 

 an elaflic fluid making its way through the oil. The only care necefTary will be, not to put 

 fo much oil into the tin rim as to occafion it either to flow over or into the jar, on a change 

 taking place in the prefTure of the atmofphere. The mouth of the vefTel fhould alfo be 

 ftopped, to prevent any of the oil from being thrown into it on removing the cover. 



In the laboratory, a thoufand ufes of thefe modes of preferving different fubRances mufl 

 occur; and it feems not improbable that, if they were extended to the purpofes of ordinary 

 life, and glafs veflels fubflituted for the porous earthen-ware at prefent in ufe, feveral ar- 

 ticles of culinary preparation, fuch as pickles, prefervcd fruits, potted meats, and the like, 

 would receive lefs injury from the efTeds of time than they are now found to do. 



* I-avoificr ufcd mercury for a fomevvhat fiinilar purpofe, but Its depth was confidorably greater. It feems 

 from fomt experiments of Pricftley's, in whith he found Ins gufc, rnmaminated with atmofpheric air, though 

 ihe tubcj had l,ccn immerfcd to the depth of an inch or more in this fluid, that, in a thin ftratum, oil would be 

 more tStiXuA. V. 



If thii conftruaion, as I undcrftand it, be fuch as to admit the oil into contaft with the rcfinous cement, this 

 lad will foon become foft by the procefs of folution. To prevent tliis effcdt, I fiippofc it would be convenient 

 to fallen llie rim by a mixture of plufttr of Paris and v.liite of cjjg. N. 



2. PreferViitlon 



