SCIENCE- G OSSIP. 



need of an improved edition of Hudson and Gosse. 

 Since writing the earlier part of this paper I have 

 become acquainted with E. F. Weber's "Fauna 

 Rotatorienne du Bassin de Leman," published in 

 1898. This excellent work, with its beautiful 

 plates, complete in every minute detail of any 

 importance, together with exact and careful his- 

 torical and descriptive remarks, very clearly shows 

 what might be done in perfecting and bringing up 

 to date a very important work. As the Hudson 

 and Gosse monograph stands, it too often leads 

 the student into wrong paths. Re-edited, it might 

 be an infallible guide to students of the Rotifera. 

 The accompanying illustration of P. platiptera 



THE CHEMISTEY OF CHROMATE 

 PRINTING. 



By Lewis Ough, F.C.S. 



1. The Carbon Process. 



THE term " carbon printing " is applied to those 

 methods in which a pigment that may be, and 

 often is, carbon or charcoal is incorporated with 

 gum, albumen, gelatine, or other organic substance, 

 and applied as a coating to the paper. This " plain 

 tissue " is sensitised by treatment with a neutral or 

 slightly alkaline solution of potassium bichromate, 

 or a solution of this salt may be added to the 



Flu. 3. Dyaschiza simiaperta Gosse. Drawn from life by W. Wesche. 

 a. Lateral view. b. Dorsal view. c. Diagram of tropin, latera 1 . </. Diagram of tr Jpbi, dorsal. 



is drawn from a specimen T ggth of an -inch in length 

 on the body, and is a dorsal view. Notommata 

 laoinulata (Ehrenberg) .is gfgth of an inch long. The 

 drawings show the Dyaschiza markings on the 

 sides and back, the setae on the toes, the dorsal 

 and lateral antennae, and the muscular structure 

 of the gizzard. The diagrams of the mastax are 

 approximate to explain its method of work, and 

 are not drawn from specimens with the soft parts 

 dissolved in caustic potash. Dyaschiza semiaperta 

 Gosse is drawn from a specimen ^ l 3 th of an inch long, 

 and the remarks on 2F. laoinulata apply to it also. 

 The three species can be "dipped" in almost any 

 pond round London. 



90 Belsize Road, London, N. W. 



organic mixture with which the paper is coated. 

 As, however, after being sensitised its keeping 

 properties are said to be uncertain and variable r 

 the worker is recommended to sensitise the pig- 

 mented tissue as required. The tissue thus pre- 

 pared must be very carefully protected from light 

 and moisture. 



Munro Ponton, of Edinburgh, noted many years 

 ago that certain organic bodies, notably gelatine,, 

 if treated with a chromic salt such as potassium or 

 ammonium bichromate, and, spread on paper or 

 other medium, dried and exposed to the action of 

 light, are no longer soluble in warm water. It is: 

 due to this chemical fact alone that the process of 

 carbon printing has been developed. The bichromate 



