44 



MR J. Y. BUCHANAN ON THE 



Table B. 

 Observed Total Weights of Hi/drometers tvhen floating .at the bQ-mm. mark 

 in Distilled Water at various Temperatures. 



Hydrometer. 



Temperature. 



Mean Total Weight. 

 Grams. 



Number of 



Series of 



Observations. 



Maximum Departure 

 from the Mean. 



Probable Error of 

 Arithmetical Mean. 



17 



15-00 



181 8304 



10 



0049 



+ 



0-0006 





19-50 



181-7105 



16 



0-0023 



0-0002 





23-00 



181-5952 



12 



00093 



0-0010 





26-00 



181-4785 



9 



0-0074 



00008 



21 



15-00 



188-7012 



12 



0-0085 



0-0007 





19-50 



188-5767 



16 



0-0040 



0-0003 





23-00 



188-4570 



15 



0-0107 



0-0011 





26-00 



188-3363 



9 



0-0031 



0-0005 



3 



15-00 



179-3116 



12 



0-0117 



0-0012 





19-50 



179-1987 



12 



0-0040 



0-0005 





23 00 



179-0757 



4 



0-0006 



0-0001 





26-00 



178-9697 



16 



0-0038 



0-0002 



Section III. — Determination of the Specific Gravity of a Saline Solution. 



§ 18. When determining the specific gravity of a saline solution by the hydrometric 

 method, it is necessary first to find the weight which must be added to the hydrometer 

 to immerse it to the 50-mm. mark when floating in the saline solution at the 

 chosen standard temperature. This added weight is found by a series of observations 

 in exactly the same manner as with the hydrometer in distilled water (see § 14 ei seq.). 



The details of three series of observations with hydrometer No. 17 in a solution 

 of \ gram-molecule of csesium chloride in 1000 grams of water at 19 "50^ are given 

 as an example in Table C. This table is arranged in the same manner as Table A^. 



The correction for the difference of the mean immersion from 50 mm. is calculated 

 in the same manner as has been explained in connection with the determination of the 

 displacement of hydrometer No. 17 in distilled water. 



Taking the series XX. 79 as an example, we find that an increase of O'S gram in 

 the added weight increases the stem immersion from 6*0 to 93*5 mm., that is, 

 87 '5 mm. ; hence each mm. increase in the stem immersion is caused by an addition 

 of 0*800/87'5 = 0'00914 gram. The difference of the mean reading from 50 mm. in 

 the series in question is 50 — 49'62 = 0*38, which is equivalent to an added weight of 

 0-00914 X 0-38 - 0-0034 gram. 



As the mean reading is less than 50 mm., the hydrometer is not sufficiently 

 immersed in the solution ; therefore the added weight is too small and must be in- 

 creased. The weight to be added is 0'0034 gram; the resultant weight which must 

 be added to the hydrometer to immerse it to the 50-mm. mark in the solution at 

 the mean observed temperature is therefore 3-7 -H 0'0034 = 3 7034 grams (line o). 



