Paul Haas and T. G. Hill 359 



From these figures it will be seen that whereas the melting point of 

 a 3 per cent, solution is approximately the same for both substances, 

 the melting point of a 5 per cent, solution of carrageen is considerably 

 higher than that of a 5 per cent, gelatine, and that, so far as physical 

 properties are concerned, a 5 per cent, carrageen could be used for slope 

 or plate cultures, without fear of liquefaction in incubators at or slightly 

 above blood heat. 



The only published observations on the melting points of carrageen 

 which we have been able to trace are those of Standford 1 who compared 

 the gels obtained from various seaweeds with gelatine. He gives the 

 melting point of a 3-2 per cent, solution of gelatine as 15-5° C. and that 

 of a 3-6 per cent, solution of carrageen as 21° C. These figures are 

 markedly different from those recorded above ; it is, however, impossible 

 to examine them critically since Standford gives no information re- 

 garding his methods. 



The gelatinising property of carrageen is not destroyed by boiling; 

 thus a 3 per cent, aqueous solution of carrageen boiled for 3| hours 

 under a reflux condenser sets on cooling after a few minutes whereas 

 a 3 per cent, gelatine solution similarly treated does not set for several 

 hours. 



Hygeoscopic Properties. 



The dried plant and also the scale preparations of the aqueous 

 extract of the plant are markedly hygroscopic. Very varying figures may 

 be obtained according to the atmospheric moisture obtaining at the 

 time of the experiment. 



For the air-dried weed figures varying from 2-54-18-2 were obtained. 

 Other authors give varying figures; thus Church 2 found 18-78 per cent, 

 of moisture in the air-dried plant, Jolles 3 12-36 per cent, of moisture, 

 and in Thorpe's Dictionary of Applied Chemistry the value 17-9 per cent, 

 is given. 



In order to compare the hygroscopic properties for hot and cold 

 water extracts of the weed determinations were carried out concurrently 

 on these materials with the following results. 



Cold water extract ... ... 23 % moisture 



Hot water extract of residue ... 19% ,, 



Direct hot water extract of weed 21 % „ 



1 Standford, Pharm. Journ. 1884, xiv, 1010. 



2 Church, A. H., Journ. Bot. 1876, xiv, 71. 



3 Jolles, M. and A., Just. bot. Jahresber. 1896, n, 452. 



