364 A. W. Ewell — Rotatory Polarization. 



neither drying up nor putrefying, The proportion most 

 suitable for the majority of the experiments was l g gelatine, 

 5 CC water, 5 CC glycerine in warm weather, and in winter a little 

 more glycerine and water. A greater proportion of glycerine 

 to water makes a slimy jelly, less of the nature of a rigid, hard 

 body. The stiff est jelly which is still sufficiently transparent 

 consists of l g gelatine, 2£ cc water, 2£ cc glycerine. The mix- 

 ture of gelatine, water and glycerine was heated at about 100° 

 C. until the gelatine was completely dissolved, which usually 

 required nearly an hour. 



Jelly Tubes. — Most of the experiments described below were 

 performed with jelly in rubber tubes. A different form of 

 tube was used from that of the earlier papers. A proper 

 length of proper sized pure rubber tubing was chosen and a 

 brass tube about 3 cm long, the external diameter of which was 

 slightly larger than the internal diameter of the rubber tube, 

 was slipped into each 'end of the rubber tube for about l cm , a 

 circular glass disk slightly larger than the brass tube being 

 pushed in ahead of the brass tube. The tube was then com- 

 pletely filled with the melted jelly through a slit in the side. 

 With patient manipulation air bubbles could be avoided. The 

 glycerine jelly was so tough that it was not necessary to close 

 the slit with wax. The rubber tube was bound upon the brass 

 tube with wire ; unless otherwise stated, the internal diameter 

 of the rubber tube was 114 cm and the external diameter of the 

 brass tube l*42 cm . This style of jelly tube, which will hence- 

 forth be designated as a " jelly tube," is greatly superior to the 

 former style where square glass plates were directly cemented 

 to the rubber tube, in that the brass tube could be grasped 

 with far less distortion of the tube and afforded far more 

 opportunity for adjustment than the glass plates. 



Independent Jelly Cylinders. — These were constructed by 

 pouring melted jelly into a test tube, allowing the jelly to set, 

 then plunging the test tube into hot water which melted the 

 jelly next the glass, allowing the cylindrical core to slip out. 

 A suitable length was cut off with a sharp knife ; short lengths 

 of slightly smaller rubber tubing (internal diameter l*76 cm ) 

 were slipped over the ends for about 7 mm . A glass disk was 

 placed against each end inside the rubber tubing and a brass 

 tube slightly larger than the rubber tubing (external diameter 

 1*90) was then pushed into the rubber tube up to the glass 

 disk. The brass tubes were grasped in the clamps by which 

 the twist was applied. These independent jelly cylinders were 

 similar to what the jelly tubes would be with the central part 

 of the rubber tube cut away. The jelly cylinder must be of 

 exactly the popular diameter. If too large the rubber tubing 

 is quite likely to cut it and if too small it is likely to slip in 

 the rubber tubes. 



