118 



one of the lifting pieces of ihe key, will confift in the aflual 

 opening of the lock ; and this cannot be had unlefs the due 

 length of ail the pins be obtained at once ; againft which the 

 probability will be as the number of permutafions of the pins, 

 multiplied into the number of poffible lengths of pins pra6^ically 

 differing from each other in efFect, Thus if the pins were fix, 

 the permutations would be 1 x 2x 3 x 4.x 5 x 6=720 ; and if 

 the length of a whole pin were one quarter of an inch, and a 

 fenfible difference would in pra6lice arife from making the 

 pins one-fi>s.tieth of an inch longer or fliorter, there would 

 be 15 poffible lengths for every pin. Whence 720x 15 = 

 10800, the number of chances againft the (iifcovery. 



W.N. 



XVT. 



On the Cuvfe of the different Colours r.f the Triple Sets of Platina, 

 and on the Exifience (f a neiv Metallic Suhftance in that Metal. 

 jSjCollet-Descotils.* Frefented to the Clafs of Mathe- 

 matical and Fhi/fical Sciences of the National Inftitute of 

 Fiance. 



Precipitation of IXLL chemifts know^that crude platina is eafily foluble only 

 the folution of j,j nitro-muriatic acid, that the folution is decompofable by 

 muriate of ammonia and other falts with alkaline bafes; and that 

 > the refult of their former decompofuion is a triple compound, 

 confining of oxid of platina, muriatic acid, and ammonia, or 

 the alkali employed. The colour of this precipitate varies from 

 a light yellow to a dark brown. It is (ometimes alfo greenilh. 

 The latter is the cafe if the folution of platina is precipitated 

 by a fait with bafe of foda. 

 Remavks. Before I fay any thing further concerning the caufes which 



influence the colour of this precipitate, I (ball point out fome 

 phenomena which charaderife the folution of the metal itfelf. 

 Foreign admix- The grains of platina of commerce always contain more or 

 tuies in crude j^j-^ ^^ foreign mixtures from which it fliould be previoufly freed 

 as much as poffible. The foreign bodies met with are mofi; fre- 

 quently minute ftones, on which the acid employed fordifiblv- 

 ing the metal, has little or no a6lion, and two forts of ferrugi- 



* Gehlen's Chemical Journal, Vol. II. Part I. p. 73. 



nous 



