166 MK J. Y. BUCHANAN ON THE 



In the first vertical columii the line corresponding to each item is designated by 

 a letter — a, h, etc. In the second column are the symbols used for the principal items, 

 and in the body of the scheme the items are described or explained. 



At the top of the table the standard temperature, T, selected for the experiment is 

 given, along with the designation of the liquid experimented on. 



The descriptions in the scheme explain all the items, but we may refer more 

 particularly to one or two of them. 



In lines d and k we have the times of the beginning and end of the experiment. 

 These are important, not only with a view to ascertaining the duration of the experi- 

 ment, but also as a matter of routine in all laboratory work. It is often of great 

 importance in the discussion of the results of experiments to know if errors which 

 appear to be possible, or indeed probable, could in fact have occurred in the time or in 

 the order in which the experiments were made. 



Lines e and^, the initial and final temperatures of the liquid. As above indicated, 

 these should be identical, and the condition Ti = Ty = l'' should hold. The thermometer 

 chiefly used in these experiments was one graduated on the stem into tenths of a 

 Centigrade degree, the length of the whole degree being 12 millimetres. This is a very 

 suitable type of thermometer for the work. 



Lines y* (f^, f=^, etc.). Each of these lines contains two entries in each series, namely, 

 %v^ the " added weight " in grams, and E, the corresponding division, in millimetres, on 

 the stem, at which the hydrometer, when so loaded, floats in the experimental liquid. 

 The addition of external weights proceeds usually by increments of 0"1 gram, and when 

 distilled water was the liquid, and hydrometer A was being used, each such increment of 

 weight produced an average increment of immersion equal to 10'69 millimetres, so that 

 nine observations could be made in each series. In concentrated solutions as many as 

 eleven single observations could be made in one series. The initial added weight was 

 regulated so that the fifth or middle reading should approximate closely to the 50-mm. 

 division, which was the arbitrarily selected division on the stem for the average 

 immersion of the hydrometer in every series. 



By dividing the difference between the first and last of n readings by n — 1 we 

 obtain the mean immersion produced by O'l gram, which is given in the line g, and we 

 are thus able to determine the displacement of each millimetre of the stem. 



Lines n and o. Line n contains the correction, dw„ to be applied to the mean 

 added weight w in order to make R = 50 mm. ; and line o gives w + dw,., the total 

 added weight when the hydrometer floats at 50 mm., the temperature being T. 



Lines p and q. These lines contain the correction, dLVt, to be applied to the 

 mean added weight w, to compensate for the difference dt of T from the standard 

 temperature T. 



Line r. This line contains the sum w + div,. + diVt, which is the total added weight 

 which would immerse the hydrometer to 50 mm. when floating in the liquid having 

 the temperature T exactly. 



