REPORT OF CHEMICAL LABORATORY 237 



If heated after solution had been completely effected the reduction was found to be much 

 less, and in many cases practically nil. 



A solution of Kordofan gum made at 90° indicated a viscosity of 10 degrees retardation. 

 The same gum dissolved at 32° and then brought to 90° showed a viscosity of 11. 



Effect of Dilution. — A solution of given strength made by dissolving the gum in the ^"^^^ °' 



dilution 



requisite quantity of water will have a higher viscosity than one made by diluting a stronger 

 solution to the same point. The difference in viscosity is slight in most cases, but in some it 

 is considerable. Thus: — 



Retardation in angular degrees. 

 Solution made Solution made 



Bas du fleuve No. 1 



„ No. 2 



„ No. 3 



Galam „ No. 3 



., No. 12 



Salabreda 



Finally, the viscosity of gum solutions is very much affected by the temperature at 

 which the observations are taken. The liquid should not vary more than about a quarter of 

 a degree Fahrenheit from the temperature chosen for the comparisons. 



Method of preparing Gum Solutions for Viscosity Determinations. — The Method 

 moisture having been determined by heating the powdered gum to constant weight in an air 

 oven, at 105° to 110° C, an amount is weighed out equivalent to 40 grammes of the dry gum. 

 This is placed in a bottle of 250 c.e. capacity and sufficient water weighed out in a beaker to 

 bring the total weight to 200 grammes. The gum is well mixed with the water by means 

 of a rod provided with a well-projecting rubber tip, until no more particles can be seen. The 

 bottle is then closed by means of a perforated rubber stopper through which the rod passes, 

 and the mucilage allowed to stand for 5 or 6 hours. If a 30 per cent, solution is made the 

 solution should be allowed to stand over night. 



The distilled water used for solution should be at about the temperature at which the 

 observation is to be made, and the mucilage should be well mixed again before it is brought 

 to the standard temperature and tested. 



TUREBA 



An earth of this name is very generally used in the Sudan as a remedy for syphilis. 

 The most highly prized is that from the vicinity of Berber ; and the wonderful effects 

 ascribed to it are attributed to the presence of mercury. How this idea originated is not 

 known — probably simply by inference from its supposed anti-syphilitic effect. So general 

 is the belief in the presence of mercury that the native hakims even employ small cones for 

 treatment by fumigation. 



Five different samples of tureba were purcliased in the Onidurman market. Although Absence of 

 in most cases as much as a pound of the earth was employed in the test, not the faintest ^"'^'^'J .f""' 

 trace of mercury could be detected. The same result was had from the examination of one 

 of the fumigation cones mentioned above. Dr. Balfour reports one case in which mercury 

 was found. This sample was obtained from a native hakim and possibly the mercury was 

 added tu it. 



