35* Method of ajayn^ Fejfeh of Tin. 



or other circumftances equally uncertain. Chemical analyfis is, no doubt, capable of accu- 

 racy ; but the procefl'es are long and minute ; befides which, they require that a portiort of 

 the veffel itfelf.ftiould be taken ofF. The examination of fpeciftc gravity has none of thefe 

 inconveniences ; but to make it the foundation of a legal proof it is neceflary to know by 

 experiments in what manner tin and lead, united together in different proportions, are af- 

 fedted in this refpesS. It has been fufpv;£ted that the alloys of thefe two different metals do 

 not exa-flly poiTcfs the fpecific gravity which would refult from taking the fpecific gravities 

 of each Separately. But is the fpecific gravity greater or lefs than the refult of computation? 

 Do the two metals penetrate each other, or do their parts on the contrary leave a greater va- 

 cancy than before their union ? Experiment alone can (hew this, as the opinion of learned men 

 differ on the fubjeft. Kaeftner, Haufcn, Hahn, and even Lavoifier in his report on the 

 art of the pewterer by Salmon, were of opinion, that penetration takes place. The common 

 fpecific gravity refulting from the mixture, according to the latter, greatly exceeds what 

 Would be deduced by calculation from the volumes of the maffes. Kraft alone adopted the 

 opinion of the dilatation, in the 15th vol. of the Memoirs of Peterfburg ; but he fupported 

 his reafoning on one folitary fa<2. Thofe who have elfewhere treated this fubjeiSl, particu- 

 larly in the Memoirs of the Academy of Stockholm, have confined themfelves to compute 

 without making experiments i and confequently it became neceffary to refer the whole to 

 t)bfervation. 



The purefl tin and lead which could be procured were taken and mixed in different pro- 

 portions, with the greateft care to mix the alloy well together, and leave no cavity within. 

 Three feries.of thefe pieces were made, which were fubjeded to the hydroftatic balance, and 

 afforded the following refults. 



The alloys of tin and lead have really a lefs fpecific gravity than would be indicated by 

 calculation. Confequently, the two metals are fo far from penetrating each other, that they 

 increafe their volume when mixed together. 



The following is t'le law of this augmentation as deduced from experiment. 



When the alloy of lead was in the proportion of -^^ , and, confequently, the tin was ^, 

 the volume of the mixture was augmented, or, in other terms, the fpecific gravity was dimi- 

 niihed 26 thoufandth parts. 



8 parts of lead and 2 of tin, augmentation of volume 40 thoufandths 



7 ditto of lead and 3 of tin, - - - 48 



6 ditto of lead and 4 of tin, - - - 47 



5 ditto of lead and 5 of tin, - - - 46 , 



4 ditto of lead and 6 of tin, - - - 45 



3 ditto of lead and 7 of tin, ~ - - 43 



24 ditto of lead and 7^ of tin, * * - 39 



2 ditto of lead and 8 of tin, ~ - " 33 



ij^dittoof lead and 8iof tin, r ^ - r 3© 

 , : I ditto 



