238 Proceedings of Royal Society of Edinburgh . [sess. 
solutions of hydrobromic acid are “positive” at 15° C. and 
“negative ” at 0° C. (cf. figs. 1, 2, 3). 
Another effect of temperature is well seen in fig. 4, in which, 
for the purpose of comparison, the viscosity of water at each 
temperature is shown by a thick black line. At 0° hydrochloric 
acid alone has viscosity greater than that of water at all con- 
centrations, at 15° the viscosity of hydrochloric acid and hydro- 
bromic acid is greater than that of water, while at 25° potassium 
bromide and iodide still have viscosity smaller than that of 
water, but the one normal solution of potassium chloride has 
practically the same viscosity as water, though at all three con- 
centrations it is greater than that of water. Sprung ( loc . cit .) 
has shown that at higher temperatures the viscosity of the 
concentrated solutions becomes greater than that of water. 
