23G REPORT OK rHKMH-AI, LARORATORY 



If is this figure, repreBcnting the true strength of the gum, which is recorded in the 

 tallies on pages 2'M\ ami 2'M. 



Precaulions m I'UKCAUTIONS TO HE OHSEItVED IN DETEUMININti THE VISCOSITY OF til'M 80I,UTI0NS — 



be observed fm i 



1 lie results of numerous experiments have indicated clearly that great care must be exercised 

 to make the deteruiinations under exactly similar conditions, if trustworthv and comparable 

 figures are desired. iSlight, apparently unimportant, variations in the method of procedure 

 may be followed by very considerable alterations in the viscosity. For example, a solution 

 was made by adding water to the powdered gum, and allowing to stand, without shaking. 

 over night. The solution was tlien agitated until apparently homogeneous and tiltcred 

 twice — once through cotton wool, and again througli paper, by the aid of a vacuum pump. 

 The results of successive determinations were as follows, the figures representing the number 

 of seconds required for delivery of the same quantity, througli the same aperture at the same 



temperature : — 



First trial 



Second 



Third ., 



Fourtb 



Fifth 



Sixth 



Seventh „ 



Eighth 



An hour elapsed between the first and the sixth determination, all this time being 

 required, after filtration, before the solution had reached a condititin in which if would furnish 

 constant results. The effect was apparently connected with the fact that the gum remained 

 all night at the bottom of the flask, in a state bordering on that of a jelly. 



Temperature, not only at the time of the observation, but more especially of the li(]uid 

 at the time solution fakes place, has a very marked influence upon the viscosity of the 

 Effect of mucilage. A solution made at ordinary temperature (90- F. in tiiis laboratory) will have less 



sohirion'"'^' ° viscosity than one made of the same strength in ice cold water, and higher viscosity than a 

 similar one made with hot water, all the solutions being, of course, brought to the sfandanl 

 temperature at the time of testing. In some cases the alteration is slight, but in others it is 

 astonishingly great. The following are instances. The figures represent retardation in 

 angular degrees, in the torsion viscosimeter at 90° F. 



Variety or OuM Solution made Solution made 



Senegal " Has du flcuvo " 

 »' »• »i 



" Qrossc blanche " 



„ " Petite blanche " 



11 n M •■• 



„ " Qrosse blonde " 



II " " 



„ " Petite blonde " 



Kodofan white 



,, " blonde" 



,, ,, ... ... 



„ unpicked 



