26 REPORT OF CHEMICAL LABORATORY 



petroleuiu-other oxti-act, but in this case the colour may not appear for 36 hours or 

 more. So applied, the test is not delicate. 



The ordinary alcoholic extract of Cannabis indica of the pharmacopaiia does not 

 appear to respond to the above test ; this at least was the case with the two samples 

 examined up to the present. The explanation of this may be connected with the fact, 

 mentioned above, that the extract yielded by prolonged exhaustion with the solvent 

 does not strike the purple colour as readily as material obtained by a short extraction 

 in the cold. Then, too, the alcoholic extract of the pharniacopooia is obtained from 

 the entire flowering tops of the plant, and is therefore more complex and more liable 

 to alteration in composition than is hashish, which is chiefly the resinous matter obtained 

 by rubbing the plant tops between the hands, or by some similar method. 



[Since the above was written our attention has been called to a note on a similar 

 reaction for " cannabinol " described by Czerkis {Pharm. Post. 42, 794-5, through Ohem. 

 Zeutr. 1909, II., 1880, and abstracted in Chemical Abstracts of the Amer. Ghem. Soc, 

 Vol. 5, No. 4, Feb. 20, 1911). The note made is to the effect that potassium hydroxide 

 produces in alcoholic solutions of cannabinol an intense red colour which disappears on 

 acidifying. The extraordinarily rich purple colour obtained by the method already 

 detailed does not appear to have been obtained. 



The method as described has been in use in these laboratories for the past two years.] 



Khartoum Water- Supply 



In the last Report' a note was made on the composition of the waters of the deep 

 wells at Khartoum from which it had been proposed to take the town supply. In it 

 were recorded the results of the bacterioscopic and chemical examinations, which 

 indicated that the water was highly contaminated, and the untreated water was, in 

 consequence, condemned for such purpose. Not only were B. coli found in very great 

 numbers, but the water was found to contain notable proportions of iron and manganese, 

 sufficient indeed to give rise to the growth of crenothrix and to be objectionable in 

 Chemical notes other ways. Subsequent investigation indicated that it was possible to prevent the 

 on Khartoum contamination of the water. The means by which this was effected are detailed in 



Water-SUppIV ' nr\r^\ -r • T 1 -1 



Dr. Balfour's fuller note on the subject [virh Vol. A., page 308). It is proposed here simply 

 to give a short account of the chemical composition of the water, before and after the 

 alteration in the wells was made, by which the desired end was attained. 



The original scheme of the Department of Works comprised the sinking of seven 

 wells. These were all fairly close together — perhaps too close for efficient working. 

 At the present time only three of these wells are in use, Nos. 1, 6 and 7. At the time 

 the earlier tests were made it was not possible for us to obtain the water from each 

 well separately, so that the comparison with the present state of afl'airs is not as 

 complete as could be desired. Several examinations were made of the water of Well 

 No. 3, the results from one of these being as follows : — 



' Third Report, Wellcome Tropical Research Lahoratories, p. 399 



