MR. J. B. HANNAY ON THE MICRORHEOMETER. 
281 
It is quite evident, on examining the microrheometrical table, that the crystallic 
force has a retarding action, but what proportion of the retardation it causes could 
only be determined by examining several liquids and comparing the numbers so 
obtained with their thermal expansion curves. 
Having obtained some knowledge of the menstruum in which the salts were to be 
dissolved, an examination of the following salts was then commenced. As some of the 
substances to be examined were only slightly soluble and could not be made of normal 
strength, the effect of the amount of salt present was first investigated. Pure dry 
sodium chloride was used for this purpose, and three solutions made up—I. normal, 
II. half normal, III. quarter normal. The times taken for these three solutions at 20° 
and under 1 metre of water-pressure were— 
Probable error of mean. 
I. 
140-5 
II 
0-26 
II. 
135-9 
0-20 
HI. 
133-6 
0-22 
Water. 
131-3 
0-06 
Calling water zero, here we have an exact series in which the retardation increases 
in the same ratio as the salt present. No. III. retards by 2’3 // , No. II. by 4‘6", and 
No. I. by 9’2" ; the time is doubled in each case and so is the salt. The same law 
was found to hold good for the following salts— 
Potassic nitrate, 
,, chloride, 
,, sulphate, 
Sodic nitrate, 
„ sulphate. 
From this law it follows that any body, however slight may be its solubility, may 
be compared with salts which are soluble enough to form normal solutions. 
To find whether or not the microrheosis is affected by the crystalline form of the 
salt, the following substances were examined :— 
Formula. 
Crystalline form. 
KCI 
Cubic. 
NaCl 
Cubic. 
KNO s 
Trimetric. 
KoSCq 
Trimetric. 
The salts were dissolved to form normal* solutions, and examined at what I will 
call the standard temperature and pressure, viz. : 20° and 1 metre. The following are 
the rates :— 
* By normal solutions I mean normal as to the metal, thus K 2 SO, is halved in order to render it 
comparable with KCi, &c. 
MDCCCLXXIX. 2 O 
