822 Proceedings of the Royal Society 
consists of copper, in a solution of copper sulphate and a solution 
of one of the three chlorides, KC1, NaCI, NH 4 C1, the order is 
NH 4 C1, KC1, NaCl ; hut when the element consists of copper in 
dilute sulphuric acid and a solution of one of these three chlorides, 
the position is regular. But, owing to Kittler’s adherence to the 
' old plan of regarding salt solutions from the percentage point of 
view, and his comparing in many cases only the concentrated 
solutions, it is impossible to state definitely that the above is true. 
In the course of some experiments on the specific gravity of 
saline solutions, my attention was drawn to the divergence from the 
general rule in the case of ammonium chloride, and I made a series 
of experiments with the view of determining the cause of it. A 
portion of these form the contents of this paper. 
In the first instance, determinations were made of the specific 
gravity of aqueous solutions of various strengths of the six salts 
formed by the union of potassium and sodium, with chlorine, 
bromine and iodine respectively. The mode of experiment was 
briefly as follows : — All the specific gravities were taken at 20° C. 
in a constant temperature hath (a modification of Dupre’s) and 
referred to water at 20° as unity. Sprengel tubes were employed ; 
these after filling were allowed to remain in the hath for ten minutes: 
after weighing, some of the liquid was poured into a weighed 
platinum dish, and the percentage of salt determined by 
evaporation. Three solutions of each salt were prepared, containing 
approximately 20, 15, and 10 per cent., and these were completely 
freed from air by boiling and allowing to cool in vacuo. In the 
case of the solid ammonium salts mentioned later, the specific 
gravity after crystallisation from alcohol, or a mixture of alcohol and 
water, was taken in paraffin by means of a special form of bottle ; 
the error in experiment affecting the fourth decimal place only 
slightly. 
My determinations correspond very closely with those of Gerlach, 
made at 15° by the hydrostatic method and corrected. 
Table II. contains the results of these preliminary experiments 
compared with the specific gravity calculated from the most trust- 
worthy determinations of the specific gravity of the solid salt. 
