PHYSICS. 



By George F. Barker, 

 Professor of Physics in the University of Pennsylvania, Philadelphia. 



GENEKAX,. 



The progress of physical science during the year 188 1 has been marked, 

 especially in the department of electricity. But so intimate are the 

 relations which connect together the various branches of physics that 

 this advance has required corresponding activity in all the other de- 

 partments. 



Stas, as rapporteur, on behalf of Broch, St. Claire Deville and him- 

 self, appointed by the International Committee of Weights and Measures 

 a sub-commission on the preparation of an X-rule in ijlatinum -iridium, 

 has given a detailed account of the preparation of this rule by Matthey, 

 the eminent metallurgist, to whom they had confided the work. The 

 platinum was i^repared by precipitation from the chloride, two speci- 

 mens, each of 35 kilograms, being obtained and analyzed simultaneously 

 by Deville in Paris and Stas in Brussels. Specimen A gave 99.892 

 platinum, 0.0G5 rhodium, and 0.029 iridium 5 specimen B 99.890 plati- 

 num, 0.070 rhodium, and 0.023 iridium. A previous alloy was used to 

 yield the iridium, special care being taken to exclude metals other than 

 platinum. Onaualysis it gave : iridium, 91.100 ; platinum, 8.180 ; rhodium, 

 0.122; ruthenium, 0.120, and iron 0.012. For the alloy, 18,015.05 grams 

 of platinum, sample A, was mixed with the iridium in such proportion 

 that 100,000 parts of the mixture should contain 1,025 parts of pure irid- 

 ium ; the extra 25 parts being added to supply loss in working. The 

 liuely-divided metals were sifted thoroughly together, the powder com- 

 pressed and fused in a lime crucible. The cylinder thus obtained, which 

 was 10 centimeters in diameter and 7.5 centimeters high, was forged at 

 a white heat into a bar and rolled beiween polished rolls. It was then 

 cut into small pieces, kept in fused hydro-potassium sulphate in a plati- 

 num vessel for 3 hours, washed with boiling water and witli boiling 

 hydrogen chloride. These operations were repeated three times. Be- 

 fore the final forging three samples for analysis were taken from difi'er- 

 eut parts of the ingot. The bar, which was 45 millimeters on a side, 

 was again put under the hammer and forged into a cylinder at one end, 42 

 millimeters in diameter and 128 centimeters long. This was cut off and 



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