684 RECORD OF CURRENT RESEARCHES RELATING TO 



scope, it will be seen that its spectrum closely approaches that of 

 chlorophyll (Nos. 1, 3, 4, 5). Through a layer of two centimetres' 

 thickness a wide black band can be seen (I,, Nos. 3-5), with 

 well-defined edges, in the red from 107 to 112 between the B. 

 and C Fraunhofer lines, and three small bands less marked and 

 softened off at the edges, one (II.) in the orange between C and D, 

 from 97 to 102, another appearing very faint 'y (III.) near the yellow 

 from 89 to 91, and finally one in the green (IV.) on the left of E, 

 from 78 to 81. The second part of the spectrum is completely 

 absorbed as far as F, that is, to the limit of the blue and green. 



The .sensible difference between the spectrum of diatomine and that 

 of chlorophyll relates to band I. ; with diatomine the red band is 

 withdrawn as far as 113, whilst with chlorophyll this band stops at 

 111-5. 



A very thick layer of the solution allows nothing to pass but the 

 rays of the extreme red, and a few of the yellow ones near to D. 



The spectrum which I have just described is that which is most 

 frequently met with ; but it may happen that the bands III. and IV. 

 are not seen in the spectrum, although bands I. and II. are clearly 

 marked. These differences result, as will be seen, in a variation in 

 the composition of diatomine. 



(4) Separation of the two Colouring Principles. — To separate the 

 two colouring principles which comi^ose diatomine, Kraus and Mil- 

 lardet employ the following process * : — Some diatoms are macerated 

 in alcohol, as has been mentioned above. " After some days, when the 

 alcohol is well saturated, the solution is filtered, and into it is poured 

 from two to three times its bulk of pure benzine. It is necessary to 

 use 36 per cent, alcohol, as in this case the two liquids do not mix, as 

 would happen if absolute alcohol were used. The whole is put into 

 a flask, and strongly shaken for a minute or two, and then allowed to 

 settle. The yellow colouring principle, being more soluble in the 

 alcohol than the green, remains dissolved in it, whilst the benzine 

 takes up the green. After decanting, the alcoholic solution is treated 

 with a fresh quantity of benzine, again shaken, allowed to settle, and 

 decanted ; this operation is repeated until the benzine ceases to be 

 coloured green." To isolate the two colouring principles it is suffi- 

 cient to evaporate the solutions. 



The process of Kraus and Millardet has the inconvenience of 

 requiring a great deal of time, for which reason I prefer to employ 

 the following process, which leads more rapidly to the same result. 



I take a solution of diatomine, prepared with 90 per cent, alcohol, 

 and I dilute it with an equal volume of distilled water to diminish 

 the strength of the alcohol ; the solution does not become turbid. 

 To this mixture I add chloroform in quantity equal to one-third of 

 the total volume. After shaking it for a minute or two I leave it to 

 settle. In a few hours the separation is complete; the chloroform 

 takes up the green colouring principle, and sinks to the bottom of 

 the flask, whilst the yellow, which is more soluble in weak alcohol, 

 remains in the superficial part. After decanting, I again wash with 



* Loc. cit., p. 2(5. 



