476 Miss I. B. J. Sollas. On the Identification of [May 27, 



The chitin which had the lowest specific gravity of any I have measured 

 was that of Limulus and of Scorpio. This had a value 1*393 when cleaned as 

 above described. If, however, stronger potash is used, chitin from Astacus and 

 from Limulus approach each other in a diffusion column and give a zone at a 

 level corresponding to a specific gravity 1*398. This figure seems to represent 

 the value of the specific gravity of pure chitin, for, as stated below, it is 

 that of chitin precipitated from its solution in strong acid. 



The strength of potash which gives a common value for the specific 

 gravity of chitin from both Limulus and Astacus is 40 per cent. It must be 

 used for a short time only after the usual long boiling in 5 or 10 per cent, as the 

 prolonged action of strong potash causes chitin to become soluble in weak acid. 



Neither boiling in 50-per-cent. hydrochloric acid nor soaking in strong 

 hydrofluoric acid alters the specific gravity of chitin. 



Young chitin from a crayfish which had recently undergone ecdysis was 

 heavier than the older skin ; it formed a zone at a level corresponding to 

 a specific gravity of 1*410, with outlying pieces down to 1*420. Unfor- 

 tunately, I have not obtained the specific gravity of the cast skin. It proved 

 to be more readily soluble in weak acid after boiling potash than the younger 

 chitin and, not foreseeing this, I inadvertently dissolved it before I had taken 

 measurements. 



The refractive indices for red light of the chitin from various sources 

 which I have measured lie between the limits 1*550 and 1*557. The 

 measurement was made by Becke's method.* That from Astacus and 

 Limulus integuments lies between 1*554 and 1*557. The fluids used in these 

 determinations were aniseed oil and mixtures of aniseed and fennel oils 

 calculated to have the refractive indices 1*550 and 1*557. 



As stated above, chitin was precipitated from its solution in strong 

 hydrochloric acid, in order to determine which of the obtained values, ranging 

 between the extremes 1*393 and 1*408, represents the specific gravity of 

 pure chitin. 



The solution was performed in a refrigerator, carapaces of Astacus and 

 Limulus being used. At the end of a fortnight no difference in the bulk 

 of the solid was noticeable on inspection. The acid was then poured off. 

 and diluted in the refrigerator with 10 times its volume of water cooled 

 till a thin film of ice formed on the surface. A copious milky precipitate 

 was formed. Fresh acid was poured over the remaining pieces of chitin, 

 and slight precipitates obtained at intervals of two days from this freshly 



* "Ueber die Bestimmbarkeit der Gesteinsgemengtheile auf Grund ihres Licbt- 

 brechungsvermogens," • Sitzungsber. der K. Akad. der Wissensch.,' Vienna, vol. 102, 

 p. 358, 1893. 



