380 Perpetual Mot'iotu.— Alloy of Silver and Platina. 



applied, and the apparatus for applying it cannot be confidered as a machine for perpetual 

 motion. Neither in flriclnefs can any machine, whofe motion is derived from the motion 

 or rotation of the earth, and the confcquent change of fcafons and rotation of events, be 

 fo confidered, becaufe it does not generate, but only communicates. The perpetual flow of 

 livers, the viciflitudejfof the tides, the conftant, periodical and variable winds, the expanfions 

 and contraflions of air, mercury, or other fluids, by daily or other changes of temperature, the 

 difl^erences of expaiifion in metals by the fame change, the rife and fall of the mercury in 

 the barometer, the hygrometric changes in the remains of organized beings, and every other 

 mutation which continually happens around us, may be applied to give motion to mills, 

 clocks, and other engines, which' may be contrived to endure as long as the apparatus 

 retains its figure. 



Ufefiil Notice! reJpeBing various OhjeSls. — Silver alloyed lutth Crude Flatina.— Tempering of 

 Steel.— Rijled Shot. 



B. 



1. Silver alloyed with Crude Platina. 



BERGMAN, in his Treatlfe on the Blow-Pipe, in one of the earlier editions, dire£led 

 that the fpoon for blow-pipe experiments fliould be made of filver alloyed with one tenth of 

 platina, of which the purification was at that time little known. Dr. Lewis, in his Philo- 

 fophical Commerce of Arts, mentions the fufiou of Clver with crude platina. The metals, 

 united but imperfedly, with a remarkable projeftion of particles of the metal, as if by a 

 kind of ebullition over the infide of the crucible. Several years ago, bt^ing defirous of 

 making fuch a fpoon, I felecled ten grains of crude platina, in particles pofleffing very 

 little magnetifm, and fufed the fame with one hundred grains of pure Clver in a blafl fur- 

 nace, ufing a large proportion of nitre, with the intention of fcorifying any of the bafer 

 metals. The effect which Lewis mentions took place ; and the compound, when poured out, 

 had a fcabrous or unfound appearance. I thought the grains of platina might have been 

 merely furrounded by the adherent filver ; but this did not feem to be the cafe, for it bore 

 laminating between two fteel rollers very well. After this lad procefs, I fubjeded it. 

 to fufion again with a ftronger heat, and again laminated it into a thin plate. This 

 operation of fufing and rolling was repeatedly performed, but Hill the metal appeared 

 rough in certain parts of the furface. As a lall effort, I therefore expofed it to the molt 

 violent heat I could urge, and determined to leave it to cool in the crucible beneath the 

 nitre which flowed above ii. The crucible in the ignited ftate was taken, from fome 

 motive I cannot now recolleft, to a window, and fet down upon a tile. As I flood atten- 

 tively obferving the appearance of the metallic globule through the tranfparent and tran- 

 quil bath of nitre, the ignition gradually went off, fa as to be fcarcely vifible in that clear 

 light. But on a fuddcn it recovered itfelf in an inftant, and the nitre boiled up fo as to fill 

 the vacant fpace of the crucible. The button of metal, when cooled, was fcabrous ; but I 

 4 nevcrthcleis 



