I9I0.] 



OX THE DISTRIBUTION OF PLANTS. 



463 



Table for the Reduction of Specific Gravity at any Temperature to 

 THE Specific Gravity at 15° C. 



(Table B, Landolt-Bornstein Physikalisch-Chemische Tabellen, Berlin. 1905, 



page 323.) 



" Reducktion der Dichte d- auf die Dichte bei 15° nach den Beob. von 

 4 

 Dittmar" (Challenger Exped.), Ekman (J^ctensk. Handl., 1870), Lenz u. 



Reszof {Mem. Petersb., 1881), Thorpe u. Riicker (Phil. Trans., 166, II; 



1876), Tornoe (Norw. Atlantic Exped., 1880) berechnet von Makarof (J. 



Russ, Phys. Chcm. Gcs., 23, 30; 1891). Auszug. 



This fact shoitld be noted in connection with the use of the above 

 table, viz.. the specific gravity of a sample of sea water is the num- 

 ber representing its weight as compared with an equal volume of 

 pure water at the same temperature. The latter is usually called 

 1. 000 so that the specific gravity of a sample of sea water may be 

 some such number as 1.025. The density is the weight in grams of 

 one cubic centimeter of water at the temperature in situ (^°) com- 

 pared with that of i c.c. of pure water at 40° C. It is usually 



expressed as D-^. The salinity is the total weight in grams of the 



4 

 matter dissolved in i.ooo grams of water. 



Mathcmatic Calculation. — Through the kindness of a graduate 

 student, ]\Ir. John C. Bechtel. to whom my thanks are due, I was 

 relieved of the labor of making the mathematic calculations neces- 

 sary to reduce the hydrometric readings to 15° C. His method of 

 procedure is herewith given in a sample case. 



To determine density at 15° C. of salt water whose density at 

 23° is 1.0155. 



From the table we see that this corresponds to a solution whose 

 density at 15° lies between i.oi and 1.02. 



We therefore find figures for density of salt water at 23°, if 

 density at 15° is i.oi, and also if density is 1.02. 



Density at 20° is 1.00898 for first and 1. 01886 for second. 



