104 



KANSAS Academy of science. 



50 



40 



30 



10 



A NEW FORM OF HYDROMETER. 



BY G. H. FAILYER, 

 Kansas State Agricultural College, Manhattan. 



The writer has had charge of a large class in deter- 

 minative mineralogy, and found it inconvenient and 

 expensive to supply them -with sufficient appliances 

 for getting the specific gravity of the minerals. The 

 Jolly balance answered a good purpose, the errors in 

 its use not being greater than the variations in the 

 gravity of the minerals themselves. But the price of 

 the balance led to the wish for something equally rapid 

 and accurate, and of such price that a number of them 

 might be placed at the disposal of the students. He 

 therefore devised a combination of the Nicholson and 

 the Beaum^ hydrometers, such that the work can be 

 done with more satisfaction than with the Jolly bal- 

 ance, and the instrument is quite inexpensive. The 

 accompanying cut will fully show its form. 



It was neatly made for me by E. Greiner, of New 

 York. Its essentials, of course, are the two pans and 

 the graduated stem. The more slender the stem, the 

 less, proportionately, the error in reading. 



Its use is almost obvious from the instrument itself. 

 There is no fixed water-line, but the graduation extends 

 somewhat below the surface of the water as the un- 

 loaded instrument floats in its jar. The readings and 

 calculations are exactly similar to those made in using 

 the Jolly. First, the position of the instrument in the 

 water is noted. This is best done by reading through 

 the water (that is, at the lower instead of the upper 

 surface of the film separating the water and the air), 

 where the plane of the water cuts the stem. By this 

 means, the meniscus gives no trouble. The solid is 

 then placed in the upper pan and another reading 

 taken. A third reading is taken, this time with the 

 substance in the lower pan. The first reading sub- 

 tracted from the second will give a number represent- 

 ing the weight of the substance; the third from the 

 second, the displaced water. The gravity is then 

 found in the usual way. 



By making the stem small, the accuracy of the in- 

 strument is increased. In a comparison of one with 

 the Jolly balance, I obtained these results with the 

 same piece of barite: With the Jolly, 4.519, 4.523, 4.471, 

 average 4.504, greatest difference .052; with the new 

 hydrometer, 4.472, 4.475, 4.460, average 4.469, greatest 

 difference .015. But it is not claimed that results are 

 more accurate by this instrument than by the Jolly 

 balance. It is cheaper and more convenient. I have 

 observed that where both are accessible to students. 



tliey will use the hydrometer in preference to the balance. 



