682 RECORD OF CURRENT RESEARCHES RELATING TO 



liave nevertheless been confirmed by the spectroscopic observations of 

 M. Nebelung in his study of the colouring matters of some fresh- 

 water Alga3.* 



It was reserved for MM. Kraus and Millardet j to make known 

 the true nature of the pigment of the Diatomaceae. They succeeded, 

 by means of benzine, in separating from the alcoholic solution of 

 diatomiue two colouring principles ; one giving a fine golden yellow 

 solution and possessing all the properties of phycoxanthine, discovered 

 by the same authors in the Algfe of another group ; the other giving 

 a green solution having properties identical with tliose of chloro- 

 phyll Kraus and Millardet drew this conclusion from their obser- 

 vations, that diatomine is formed of a mixture of cldorophjjll and 

 -pliycoxan thine. 



When an alcoholic solution of diatomine is filtered, a fact very 

 simple in itself gives a proof of the presence of two colouring 

 principles. If the filtering paper used is allowed to dry, we see a 

 broad coloured border formed round the margin ; the outer part being 

 tinted yellow while the inner is green. 



To conclude the historical part I will cite the direct spectrum 

 analysis made in 1869 by Professor H. L. Smith of New York,J by 

 means of the microspectroscope. The spectrum obtained with the 

 small portion of endochrome from a single diatom, a Navicida, showed 

 the absorption-band in the red and complete absorption of the second 

 part of the spectrum, without intermediate bands. This spectrum 

 would seem to correspond with that of phycoxanthine. (Fig. 54, 

 No. 2.) 



(3) Diatomine. — Let us now see what are the physical properties of 

 diatomine and of each of the elements of which it is composed. 



A concentrated solution of diatomine, prepared according to the 

 process indicated above, has a green colour verging on brown if 

 examined by transmitted light. This colour may be more or less 

 deep. We shall see further on to what cause must be attributed 

 this variation in the tint. By reflection the same solution has a 

 carmine red fluorescence nearly resembling that of chlorophyll. 



Concentrated sulphuric and hydrochloric acids give to the 

 solution of diatomine a tint of an intense bluish-green, and different 

 from that which the solution of chlorophyll takes with the same 

 reagents. 



Ammonia gives no apparent reactions. Lime-water, and especially 

 baryta-water, render the solution of diatomine turbid, without produc- 

 ing any precipitate similar to that obtained with the solution of 

 chlorophyll.§ 



If a concentrated solution of diatomine is examined by the spectro- 



* " Spectrosk. Untersuch. des Farbstof. einig. Siisswasser-Algen," ' Bot. Zeit.,' 

 June 21, 1878, pp. 394-395. 



t " Etudes sur la matiere colorante des phycochromacees et des diatomees." 

 (Extract from ' Me'm. Soc. Nat. Sci. Strasbourg,' vi. 1868.) 



X ' Sillimaii's Journal,' vol. xxxviii. (1869) p. 83. 



§ Sec for furtlier details Ad. Weiss, 'Zum Bau uud dcr Niitur der Dia- 

 tomaceeu,' p. 115. 



