470 Mr. G. Mattbey. On the Platinum Series. [Apr. 3, 



qu'on rencontre dans la fabrication d'nne regie geodesique, et nous 

 vous prions de recevoir l'assurance de nos sentiments les pins dis- 

 tingnes. 



" Betjnner Feeres." 



In the year 1876 the suggestion was made to supersede the rec- 

 tangular form by a tubular one, and I was requested to produce one 

 of the following dimensions : Length, 1,002 centims. ; exterior diameter, 

 37 millims. ; interior diameter, 35 millims. ; with rounded ends, one 

 having an extension of small tube 4 millims. exterior diameter, 

 2 millms. interior diameter, 40 millms. long, which I did by the 

 system of tube making with autogenous joints adopted by me with 

 excellent results for the last 20 years, employing for the purpose an 

 alloy prepared as above described. These proved to be so satisfactory 

 that I have since made others, both round and square, of various 

 dimensions, as lately shown at the Paris Exhibition, 



Iridio-platinum alloy has now been proved to possess the following 

 among many advantages for standard rules and weights : — 



It is almost indestructible, has extreme rigidity, especially in the 

 tube form, and a most beautifully polished surface can be obtained 

 upon it ; its coefficient of elasticity is very great, whilst for standard 

 weights its high density is a valuable quality, and for these I should 

 indeed recommend an alloy of not less than 20 per cent, of iridium. 

 I lately made at the request of M. H. Sainte- Claire Deville a cylinder 

 40 millims. by 40 millims. of such an alloy, which showed by analysis 

 the following proportions) : — 



Platinum 80*6600 



Iridium 19 -0786 



Rhodium -1220 



Ruthenium ■ 0460 



Iron -0980 



100-0046 



and gave the density of 21 ■ 614. 



With such a high density its coefficient of elasticity is 22 ' 200000, 

 one of the highest known, whilst its malleability and ductility are 

 almost without limit. 



The volume of the kilogram thus prepared is only 46*266 cub. 

 cemtims., it displaces 2 "267 cub. centims. less than the kilogram of 

 the archives of France, and on this account, as on many others, 

 is of course preferable. 



The results I have arrived at in preparing alloys of higher grades, 

 viz., 25 — 30 — 40 and 50 per cent, of iridium, are as follows : — 



The alloy of 20 per cent, iridium is, as I have stated already, mal- 

 leable and ductile. 



25 per cent, can only with great difficulty and waste be worked 



