1889.] Physical Properties of Iron at a High 1 emperature. 87 



Corrections in the Weighings. 



The balance used could be read directly to ¥ ^ milligram, and bad 

 been proved to be a most reliable instrument. The weigbts were an 

 excellent set by Staudinger of Griessen, and showed an average varia- 

 tion from the normal amounting to only O000035 gram. 



Corrections were introduced — 



(a.) For the weigbts. 



(&.) For displacement of air and variations in temperature and 

 pressure. 



(c.) For variations arising by reason of the different hygroscopic 

 conditions of the desiccator and balance case. 



In any case where condensation of moisture was liable to occur this 

 was corrected for by noting the increment of weight per minute for 

 several minutes whilst exposed in the balance case, and then con- 

 structing a curve, with increment of weight and time as ordinate and 

 abscissa, from which the necessary correction at the time of weighing 

 could be introduced. In nearly all cases over 2 grams of the sulphate 

 was used for each determination, and even with 2 grams a difference 

 of 1 milligram in the weight of the zirconia obtained implies a dif- 

 ference of 0*25 in the atomic weight ; it is, therefore, evident that in 

 some previous determinations, where less than a gram has been taken, 

 there is considerable risk of error in the atomic weight. 



IV. " Magnetic and other Physical Properties of Iron at a High 

 Temperature." By John Hopkinson, F.R.S. Received 

 April 16, 1889. 



(Abstract.) 



This paper deals with the same subjects as are dealt with in three 

 short papers* already read before the Royal Society. It gives full 

 particulars of the experiments made both, on the samples there men- 

 tioned and on other samples. 



V. " Determining the Strength of Liquids by means of the 

 Voltaic Balance." By G. Gore, LL.D, F.R.S. Received 

 April 17, 1889. 



* 1. " Magnetisation of Iron at High Temperatures." (Preliminary Notice.) 

 ( Roy. Soc. Proc.,' vol. 45, p. 318. 2. " Recalescence of Iron." Ibid., p. 455. 

 3. " Electrical Resistance of Iron at a High Temperature." Ibid., p. 457. 



