Some Physical Properties of Nitric Acid Solutions. 91 



bubble in the glass itself, situated a few millimetres above the mark, 

 was taken as a more convenient standard of reference ; the distance 

 between the lowest part of the bubble and the best defined limit of the 

 adjustment mark was measured once for all. The water level was then 

 adjusted so that the top of the meniscus was at this ascertained 

 distance, and a weighing of the water contents made (temperature 

 24 '2) ; in subsequent experiments the water level was purposely 

 adjusted 1'6 mm. below and 1 mm. and 2 mm. above the standard 

 mark, both series being required as the capillary limb was not a true 

 cylinder. 



The following results were obtained : 



These differences in the water contents would cause differences of 

 0-00008, - 0-00002, and - 0'00005 respectively in determinations of the 

 acid of 44'1 per cent, concentration (vide infra), which would be either 

 diminished or increased by one or two units in the case of acids of 

 100 per cent, and 10 per cent, concentration respectively. 



Correction jor Displacement. All the weighings for the determina- 

 tions were reduced to a vacuum according to the usual approximate 

 formula 



W = ,!-- + -, 



V P v) 



wherein A. = 0'0012 is the adopted standard density of air under 

 average conditions, and p taken as at 8 -4; the circumstance that the 

 smaller weights were of platinum instead of brass affects the results 

 beyond the limits of experimental error and can therefore be neglected. 

 The densities were throughout reduced in terms of the maximum 

 density of water at 4 C. 



Thirdly. Temperature. The temperature was recorded by a thermo- 

 meter, graduated to O'l C., and of such an open scale that 0'03 C. could 

 be read without difficulty ; the zero displacement and the stem errors 

 of the instrument were determined in our previous investigation. 



With a view of ascertaining if there existed any appreciable error 

 in the thermometer (by Casella) used, and to examine the accuracy of 

 the method, the density of a sample of 44-10 per cent, acid (selected 

 as approximately the mean of water and 100 per cent, acid), was 



