834 OYSTERS, AND ALL ABOUT THEM. 



. The character of the water has an impor- 

 tant, if not the most important, influence upon the life of 

 the oyster. Chemical analyses are desirable, and in some 

 cases necessary, but, generally speaking, the determination 

 of the specific gravity of the water provides a sufficiently 

 accurate standard for forming either comparisons or 

 opinion. 



The investigations of the Coast Survey in Tangier and 

 Pockomoke Sounds, tributaries of Chesapeake Bay, and 

 probably the largest oyster grounds in the world, have 

 indicated 1.0140 as the standard specific gravity, i.oooo 

 indicating the density of distilled water at 60 degrees F. 

 The investigation also showed that the specific gravity of 

 those waters could fall considerably below the standard 

 without serious effect, and Count Pourtales, who investi- 

 gated the subject many years ago, came to the conclusion 

 that oysters would live in water of as low specific gravity 

 as i.ooio, which is .013 below the standard here accepted. 

 Indeed, within reasonable limits, it is not so much the 

 absolute specific gravity as it is the rate and range of the 

 fluctuations which must be considered, for oysters can be 

 accustomed to water of very great or little density ; but 

 water that changes rapidly from a high to a low specific 

 gravity, or the reverse, will soon destroy the animals. 



In determining the specific gravity of the water, the 

 delicate hydrometers, devised for this purpose by Professor 

 Hilgard, late Superintendent of the U.S. Coast and Geo- 

 detic Survey, have been used. Three are necessary to 

 cover the ordinary variation between sea and fresh water. 

 They are described in the Report of the Coast Survey for 

 1874, Appendix 16. 



. . . . All readings of the hydrometer have been 

 reduced to the standard temperature of 60 degrees F." 



