TRANSACTIONS. 



I. — Experimental Researches on the Specific Gravity and the Displacement 

 of some Saline Solutions. By J. Y. Buchanan, F.R.S. 



TABLE OF CONTENTS. 

 SECTION I. 

 Introduction. 



PAR. PAGE 



1. The Principles of Archimedes. Tliey embody the fundamental principles of the hydro- 17 



meter. Archimedes considered the immersion of a body in only one fluid, but the 

 principles hold good when it is immersed in more than one fluid. 



2. Hydrometer suitable for Demonstrations on the Lecture Table. It was constructed originally 17 



in the year 1871 for use in tutorial classes in the University of Edinburgh, and especially 

 to exhibit the determination of the specific gravity of solids lighter as well as heavier 

 than water. A remarkable feature of the instrument is that no determination of 

 weight is required either in its construction or its use. The only measurements made 

 are those of length. 



3. Usefulness of the Hydrometer in the Study of Mineral Waters. It suggested itself while 19 



working as student and assistant of Fresenius (1863-1867), and later as Chemist and 

 Physicist of the C/iallenger Expedition, during which it was used in investigating some 

 mineral waters in the Philippine Islands. 



4. The Hydrometer in the " Challenger " Expedition. Early preparations for work in the 20 



expedition which lasted three and a half years. Indirect methods rejected. Adoption 

 of the hydrometric method for determining the specific gravity of the water of 

 the ocean. 



5. In designing the hydrometer, units in the fourth place of decimals were to be exact, and 20 



the exactness to be pushed as far as possible into the fifth place. Multiple sets of 

 hydrometers rejected. One suitable hydrometer was designed, and its weight could 

 be altered by the addition of accessory weights. 



6. The series of accessory weights prepared enabled the determination of the densities of all 21 



sea-waters, up to and including that of the Red Sea, to be made with the same glass 

 hydrometer. But in the design of the series only single observations were contem- 

 plated. Duplicate observations were occasionally obtained. The volume of the 

 hydrometer was determined by floating it in distilled water at different temperatures. 

 TRANS. ROY. SOC. EDIN., VOL. XLIX., PART I. (NO. 1). 1 



