234 DR, ORD. 



of colloids — the ceaseless rearrangement of their constituent 

 elements, which made Graham call colloids the dynamic form 

 of matter — suggested that they must be the seat of infinite 

 molecular movements or vibrations, such as would tend 

 actually to break the lines of crystallisation. Clinging still 

 to the old notions of chemical fixity, holding still to the idea 

 that when the composition of a given colloid was once accu- 

 rately written down in equivalents, its position was decidedly 

 established, I had forgotten that these complex substances 

 had in each case a natural history, a story of metamorjDhosis 

 which must draw into its pages a record of rearrangement of 

 any inert stuff thrown into the meshes of the colloid. Already 

 I had used words and expressions which, as they seemed 

 most appHcable to the processes I Avas watching, might well 

 have suggested to me, while I used them, that their fitness 

 rested upon their being directly true, instead of being meta- 

 phorical. '^ Grasp " and "relative strength" were expres- 

 sions of this kind. Experiments made with reference to the 

 effects of temperature bear importantly on this point. 



In some plugs prepared during the second week of Feb- 

 ruary, 1870, when very firm and strong gelatin was rendered 

 still firmer by the prevailing cold, hardly anything except 

 octohedra and their immediate derivatives (macles, &c.) were 

 found. It was then remembered that coalescence forms had 

 been abundant and well formed in the softened plugs of the 

 summer experiments ; and although experience had shown 

 that, other things being equal, a denser plug was favorable 

 to the perfection of the coalescence forms, it was now evident 

 that the vibrations of heat, and possibly of light, must be 

 looked to as likely to aid the production of spherical forms 

 by disturbing the lines of crystallization and throwing the 

 molecules into the power of the colloid. Five different posi- 

 tions were secured for strong plugs placed between equiva- 

 lent solutions of oxalate and chloride. 



1. Kitchen, mantel-piece, temperature 55° — 65° Fahr., in 

 bad light. 



2. Study, near window, temp. 35° — 56°, good light. 



3. Study, cupboard. 



4. Garden, good light, temp. 27°— 45°. 



5. Garden, dark shed. 



It was intended to take into consideration here the effect 

 of hght as well as of heat, but no decisive results were ob- 

 tained with regard to the former force. On the other hand, 

 the influence of temperature was made beautifully evident. 

 In the kitchen specimen the coalescence forms were three or 

 four times as numerous as the crystalline. In the garden 



