[M’GILL | VISCOSITY IN LIQUIDS 99 
easy to keep the temperature of the oil constant to within 0°5 degree 
during the time of the experiment : 
No. Expts. Temp. Max. Min. Mean. 
5 60°0° F, 91810 310 311°7 sec. 
5 60°5° F. 308° 4 306 SOA OM 
7 61 0° F. 305°0 300 SOPHIE 
6 70°0° BF. 209° 0 205 207°0 ‘‘ 
4 Ties 1 166 0 164 16510 
The above represent consecutive series of tests, and illustrate the 
extremes of experimental error. 
It shouid be mentioned that the above experiments were made with 
my viscosimeter in its original form, employing the Redwood nozzle. 
Among the characters which this instrument has to recommend it 
are these: (1) That it is made without soldered or brazed joints, and can 
therefore be used with safety at the highest temperatures to which 
liquids can be raised without decomposition or volatilization ; (2) The 
temperature of the liquid in the centre of the mass contained in the 
vessels is constant, even at high temperatures, to within 0°5° C. for at 
least 200 seconds, thus permitting the use of a capillary tube at these 
temperatures ; (3) The nozzles are easily changed, even when the liquid 
is very hot; (4) The insirument is easily cleaned, and has so few parts 
that it is easily kept in working order. 
In order to be able to work with a smaller volume of liquid I have 
had a smaller instrument made, using the same nozzles as the first, but 
of 3 instead of 5 inches diameter. In consequence of this it can be 
operated with 410 cbe. instead of 1,200 cbe.; and from work which I have 
done with it I am satisfied that when the time of efflux is not too long, 
its readings are practically identical with those of the larger instrument. 
The nozzles are made in three different forms, as follows : 
Form I. Form IL Formlll. 

| 



L>// mm: 
œ 
oO 
and each form is made in three sizes, viz., 35, 2, and À, inch diameter. 

It is not unlikely that the indications given by an orifice of Form I., may 
have a higher practical value, in certain cases, than those given by the 
other forms, since interior friction is a larger function of flow in this 
form; while, in Form IIL., which amounts to a thin plate, the indications 
may be of special value in yet other cases. 
