USEFUL PROJECTS. 



389 



ten on that subject were not uni- 

 fiM-m. Kaestner, Hausen, Hahn, 

 and even Lavoisier, believed that 

 penetration took place. The spe- 

 cific gravitv resulting from the mix- 

 ture, says the latter, exceeds very 

 much that which would be obtain- 

 ed by computing the volumes and 

 masses. Kraft alone, in the Pe- 

 tersburg Transactions, vol. XIV. 

 maintained the opinion of dilata- 

 tion ; but he rested it only on one 

 single fact. Those who have treated 

 this subject in other places, parti- 

 cularly in the memoirs of the Aca- 

 demy of Stockholm, have confined 

 themselves to calculations, without 

 making any experiments; it became 

 therefore necessary,above all things, 

 to have recourse to observation. 



Tin and lead, in the most perfect 

 state of purity they could be pro- 

 cured, were mixed together in va- 

 rious proportions; great care was 



taken that they should be well mix- 

 ed together, and also that no ca- 

 vity or air-bubble should be left in 

 the mixture. Three different series 

 of these mixtures were made; and, 

 upon being tried in the hydrosta- 

 tic balance, the results were found 

 to be as follows : 



Mixtures of tin and lead were 

 found to possess less specific gravity 

 than would have been obtained by 

 calculation : consequently, these 

 two metals, instead of penetrating 

 each other respectively, increase in 

 bulk, when mixed together. 



The following is the law of that 

 increase, as far as it can be deduced 

 from the above experiments. 



When the quantity of lead was in 

 the proportion of nine-tenths of the 

 whole, the bulk of the mixture in- 

 creased, or, in other words, the 

 specific gravity diminished, twenty- 

 six thousandth parts. 



8 parts of lead and 2 of tin, increased in bulk 40 thousandth parts 



ditto 

 ditto 

 ditto 

 ditto 

 ditto 

 ditto 

 ditto 

 ditto 

 ditto 

 ditto 



A much greater number of expe- 

 riments were made on the mixtures 

 in which the proportion of tin ex- 

 ceeded that of lead; and particu- 

 larly on those where the proportion 

 of tin, to that of lead, was from 5 

 to 25 or 30 per cent, they being the 

 proportions most frequently met 

 with in commerce. 



From these experiments a table 

 was constructed, by means of which 



it is very easy (after weighing a 

 pewter vessel, first in air, and then 

 in water), to determine what pro- 

 . portion of lead is mixed with the 

 tin. 



It is very true, that this method 

 does not shew the other metalswith 

 which the tin may perhaps be mixed, 

 such as copper, bismuth, zinc, and 

 antimony ; but every one knows 

 that only a very sutiall proportion of 



