45, COBNHILL, B.C., AND 122, REGENT STREET, W., LONDON. 183 



459 Twaddell's Hydrometers, so named after their inventor, Mr. Twaddell of 



Glasgow, are very largely used by Dyers, Bleachers, and Paper manufacturers, 

 the six instruments having an extended or very open scale, figured from 

 0, Water, to 170, about the gravity of the strongest Sulphuric Acid. Each 

 degree or division of Twaddell's scale being equal to five degrees of specific 

 gravity. 



460 7 Comparative Scale showing the values of Twaddell's Hydrometers, Nos. 1 to 6 

 in Specific Gravity. 



No. Twaddell's Scale. Specific Gravity. 



1 to 25 1-000 to -125. 



2 25 50- 1-125 -250. 



3 50 75 1-250 1-375. 



4 75 100 1-375 -500. 



5 100 125 1-500 -675. 



6 135 170 1-675 -850. 

 Twaddell's Hydrometers if for use in hot climates are specially tested and 



adjusted at 84 Fahrenheit at an extra cost of 6d. on each instrument. Each. 



461 Aquarium Hydrometer, for showing the density of Salt or Sea Water s - d - 



(fig. 424) . . .036 



462 Board of Trade, Marine Hydrometers, for taking the specific gravity 



of Sea Water '0 to '40 (fig. 462) 056 



463 Ditto ditto, 2 Hydrometers with very open scale, to 40 



and 20 to 40 10 



464 Sea Water ranges in Specific Gravity from-1-020 to T036, the ordinary gravity 

 varying between T026 to 1'028. Mediterranean Sea Water about T030, and that of 

 the Caribbean Sea, 1-040. The water of the Dead Sea has the extraordinary density 

 of 1-200 to 1-250, the saltest water known. 



THE SALTNESS OF SEA- WATER. Professor Chapman, of University College, 

 Toronto, says that the object of the saltness of sea-water is to regulate evaporation. 

 If any temporary cause raises the amount of saline matter in the sea to more than 

 its normal value, evaporation goes on more and more slowly. If the value be 

 depreciated by the addition of fresh water in undue excess, the evaporation power 

 is the more increased. He gives the results of various experiments in reference to 

 evaporation on weighed quantities of ordinary rain-water and water holding in 

 solution 2'6 per cent of salt. The excess of loss of the rain-water compared with the 

 salt solution was, for the first twenty-four hours, 0'54 per cent., at the close of 

 forty-eight hours, T46 per cent ; and so on in an increasing ratio. 

 Analysis of sea-water taken from the English Channel : 



Chloride of Sodium 1891-6 



Chloride of Magnesium 228-4 ' 



Chloride of Potassium 47*8 



Iodide and Bromide of Magnesium . . . 15-4 



Sulphate of Magnesia 145-4 



Sulphate of Lime 94-5 



Grains per gallon . 2423-1 



These quantities vary with the locality as well as the percentage of - Organic Matter 

 also found in Sea Water. 



The ordinary surface Temperature of the Sea in temperate climates is 45 to 

 51-5 Fahr. 



" In most parts of the world the average temperature of the ocean's superficial water is 

 nearly that of the air upon its surface. In the tropics the temperature of the sea water 

 ranges from 70 to 80 Fahr. or more, and the air is much the same. In some limited parts 

 of the globe the surface water is as warm as 86 P , for instance, near the Galapagos Islands ; 



