36 



MR J. Y. BUCHANAN ON THE 



The temperature at the commencement of the observations in our example was 1 5*00°, 

 and at the end 1 5 "02°, the mean being 15*01°. 



The departure of the mean temperature from 15*00° is, T — T = (]?i = 1501 — 15"00 

 = 0"01° (line p). Therefore the amount by which the added weight must be increased 

 for the difference dt is dwt = 0*00026 x 1 = 0*00026 gram (line q). The mean tempera- 

 ture observed during the time the observations were being made was higher than the 

 standard, so that in this case we must add the correction for temperature to the 

 added weight required to immerse the stem to 50 mm. at 15*00° C. 



y 



2600 



2300". . 



1950' 



I 



i 



15 00°- ■ 







181'hOOO 



J • 000475 gm per 0/ "C 



00035 gm per 01 "C 



00050 gm per ore 



Total Displac/ng Weight 



H 1 



■00026 gm per ore I 



5000 -6000 7000 



Temperature Curve for HyorometerN^//. 



■+- 



80 OQ 



Finally, by adding together the mean added weight, w, the weight, dw^, for 

 the difference of the mean reading, R, from 50 mm., and the weight, dWi, for 

 the difference of the mean observed temperature, T, from the standard temperature, 

 T, we obtain the weight ii; + c?w;^ + c^'M;j= 0*925 + (- 0*0064) + 0*00026 = 0*91886 gram 

 given in line r, which must be added to the hydrometer to immerse it to the 

 50-mm. mark in distilled water of 15*00° C, and by adding this weight to that 

 of the hydrometer in vacuo we obtain 180*9113 + 0*91886 = 181*83016 grams 

 (line s), which is the total weight of water displaced by the hydrometer under 

 these conditions. 



^17. The data for the determination of the total weights of hydrometer No. 17 



