^ Chemical Examhatwi ef the Bath Waters. 3f59 



I ditto of lead and g of tin, - - - 23 



\ ditto of lead and 9i of tin, - - _ 14 



.^. 

 The experiments were more multiplied for thofe mixtures in which the proportron of tin 

 exceeds that of lead ; and more efpecially when the tin contained from 5 per cent of lead to 

 a^5 or 30, becaufe thtf^ cafes offer themfelves moft commonly in afl-ual bufinefs. 



On thefe data a table is formed, by means of which it is very eafy to determine, by 

 weighing a veffel in air and in water, what proportion of lead the tin may contain. 



This method undoubtedly cannot fliew the other metals, fuch as copper, zinc, bifmuth, 

 and antimony, with which the tin may be alloyed ; but every one knows that thefe metals are 

 mixed with the pewter in the market in very fmall proportidns ; fonie becaufe they alter the 

 colour and quality; and others, becaufe the price being at leaft equal to that of tm, does not 

 render it the intertfl: of the tradefman to add tlrcm*. 



Ch. Coquebert. 



IX. 



A Chemical Examination of the Bath Waters. By G. S. GiSBESy B.M. F.R.S.\ 



X W O ounces of the King's-bath water experienced no change of colour when a few 

 drops of the fpirituous tiniiure of galls were added to it: on the addition of one drop of a fo- 

 lution of fulphate of iron, it became of a purple colour. 



The water which ferved for this experiment had been carefully preferved in a well-clofed 

 bottle. . ' 



The fame quantity of this water warm and frefh from the fprin^ experienced a coniider- 

 able change -of colour on the addition of the tinduie of galls, evidently fhewing the prefence 

 of iron. 



Under precifely the fame circumftances, the water of the two other fprings which I exa- 

 mined, viz. the Hot and the Crofs-bath waters, produced the fame appearances. 



• As it cannot be expefted that this abridged account fliould contain the various reafonlngs and precau- 

 tions of the gentlemen of the commiffion, I may, perhaps, have been anticipated on the fubjeft of the fol- 

 lowing remarks, i. The handle, and fometimes the foot, of pewter veffels are made hollow; whicli COB- 

 flrudVion, if not provided againft by the examiner, will defeat the purpofe of this proof, i. The artift may 

 leave cavities for the fraudulent purpofe of rendering his goods lighter, and confequently of a finer apparent 

 title than it really poireffes. 3. The denfity of caft-meta! varies according to the heat of the metal, and the 

 toldnefs of the mould. 4. IVIoft articles of pewter are hammered, which will increafe.the denfity, though not 

 fo much as the laftmentioned caufe. 5, The fmall additions which are made to. improve the hardnefs and 

 colour may alfo change the denfity. It is affirmed that arfenic, in particular, is very effeftual in this 

 cefpc£t N. 



J Communic«ted by the author. ' - . 



3 A a From 



