Density of Brine in Boilers of Marine Steani-Engines. 281 



cate the density is in the lower stratum, not the upper one, 

 where the usual glass gauge is placed, and irretrievable mis- 

 chief might be done before the indication would shew any 

 change. 



I have lately employed, in some large ships destined for 

 transatlantic voyages, a species of brine-gauge, or index of 

 saturation, which is found to possess every advantage, and 

 which I therefore desire to communicate to the public through 

 this Society. The drawings sent are such as may enable any 

 engineer to construct them for himself. The details of the 

 arrangement of the apparatus were made under the direction 

 of Mr James Laurie, formerly one of my assistants ; and he 

 also has obliged me by writing out the annexed description of 

 the operation of using the index. 



The principle I have used is the well-known law, " that the 

 heights of equiponderant columns of liquids vary inversely as 

 the densities of those liquids." 



If I take open glass tubes bent in the form of the letter U. 

 as in the diagram (fig. 1), and pour one fluid into one of the 

 sides, and another fluid into the opposite side (taking care to 

 use the heavier liquid before the other) ; the one being mer- 

 cury, and the other water, they will stand at the height of 

 1 inch and 13 inches respectively. If I use alcohol and water 

 (fig. 2), they will stand at the height of 10 inches and 8 inches 

 respectively, the height of the one fluid being always greater 

 than that of the other, in the proportion in which its weight, 

 density, or specific gravity is less. 



Fig. 1. 



Fig. 2. 



Fig. 3. 



Uatcr 



Waltr 



= Merruiy 



Alcohc 



Watf 



■i- 



Sail Water 



