3 Id On the Tuimvg of Copper^ 



c'retv. To decide the question in a peremptory inanner, it 

 was necestiSiT to undertake a sa'ies ot experiments which 

 had before been neglected. To succeed in tl"keni it was pre- 

 viously necessary to exaniir.e the properties of some metals 

 and oxides ; and there are nine paragraphs employed, in the 

 examinalion of iron, antimony, niercuvy, lead, and zinc. 

 This examination was requisite to answer all the objections 

 which he proposed to resolve in the third part of this work. 



PART II r. 

 This part is divided into five paragraphs. 

 Paragraph I. 

 Experiinetits made on the old Method of Tinn'mg. 

 Five plates of copper, each a foot square, were tinned, 

 all the necessary precautions being taken. The object of 

 the author wa: to ascertain the quantity of alloy ihcy would 

 lake one with another. 



The quantity of tinninij which copper can take is exceed- 

 ingly variable, and not suLject to calculation : the alteration 

 of the copper by tinning being in all points the same, the 

 variations in the weight must necessarily depend on tiie 

 wore or less exact manner in which the workman removes 

 the superfiuous tinning; and one might he niduced to be- 

 lieve that the artist has it in his power to give a tinning 

 more or less abundant ; but the tinning not alloyed with 

 the copper ought not to be considered in the same nianner 

 aithat which is alloyed. The author has proved, in gene- 

 ral, that good tiia^iing takes a grain of tin per square inch. 



Paragraph II. 

 On the Dnration and Causes cf the Destruction of Tinning. 



Tinning v.'ith pure tin has a silver white colour, and, ia 

 contact with vapours capable of attacking it, assumes a yel- 

 lowi^h tint. That made with one-third, one-fourth, or 

 one-half of lead, like the old tinning, has more brilliancy, 

 and iDay be easily distinguished from the former. 



The causes which destroy finning are friction, caloric, 

 and acids : the effects of all these causes vary according to 

 an infinite number of circumstances, which are determined 

 by the author as exactly as possible;, and have taught him, 



that. 



