1902.] 



Estimation of the Specific Gravity of Blood. 



Ill 



[Added Nov. 28, 1902. — Since this paper was communicated to the 

 Eoyal Society, I have seen a paper on the spectrum of lithium, by 

 Hagenbach, in the ' Aimalen der Physik,' No. 12, 1902, which was 

 published on November 13. The experimental part of his paper deals 

 almost entirely with the blue line, and the fact that there are other 

 abnormal lines in the spectrum of lithium is recorded above for the first 

 time. Hagenbachs conclusion that there are two lines near wave- 

 length 4603 is not, I think, established ; and I still hold that the 

 views expressed in this paper are more probable. He has not been 

 able to find the second line as a bright line, so the difficulties in the 

 way of accepting the view that there is a second dark line, without 

 a corresponding bright line, remain. He has not referred to Pro- 

 fessors Liveing and Dewar's work,* and his evidence for saying there 

 are two lines is, in fact, similar to the evidence they gave.] 



* An Error in the Estimation of the Specific Gravity of the Blood 

 by Hammersclilag's Method, when employed in connection 

 with Hydrometers." By A. G. Levy, M.D. (London). Com- 

 municated by Sir Victor Horsley, F.B.S. Received 

 November 25, — Read December 11, 1902. 



(From trie Laboratory of Pathological Chemistry, University College, Loudon.) 



Hammersclilag's method of estimation of the specific gravity of the 

 blood is an application to clinical purposes of a physical method 

 frequently employed when only a small quantity of the substance 

 under investigation is obtainable. The method may be briefly described 

 as the adjustment of the specific gravity of a mixture of chloroform 

 and benzol by small successive additions of either constituent until it 

 corresponds to the specific gravity of the blood, the test of the attain- 

 ment of this condition being that a small drop of the blood, when 

 immersed in the mixture, shall remain suspended without any very 

 obvious tendency to rise or sink. The specific gravity of the mixture 

 is then estimated by means of a hydrometer, the scale of which is 

 graduated to register densities lying between the maximum and mini- 

 mum densities of blood, i.e., from 1*020 to 1*080. 



In order to attain a rapid adjustment of the relative proportions of 

 the chloroform and benzol, it is the general practice to use a com- 

 paratively small quantity only of these fluids and a small hydrometer, 

 and, as will be hereafter seen, the size of the instrument is an 

 important factor in the magnitude of the error. 



This error was commented upon in a paper read by Dr. Baumann 



* 'Phil. Trans.,' vol. 174 (1883), p. 215. 



