Doable Refraction in Liquids. 495 



'000025 X. A fresh solution gave no effect. After the 

 solution had remained in the chest for several hours it became 

 slightly turbid, and an effect like double refraction appeared. 

 This did not become evident as soon as the cylinders were set 

 in motion, but after ten or fifteen seconds. When the motion 

 stopped, the effect disappeared in the same slow manner. 

 Mr. Almy, in 1897, observed an anomalous effect in this 

 substance. He ascribed it to the action of small particles of 

 paraffin, with which the inside of the chest was coated. 

 Before I began my work the interior of the chest and the 

 cylinders were carefully nickeled, and before these experiments 

 they were scoured. The solution was filtered before being 

 put into the chest. Neither air-bubbles nor fine particles 

 gave any effect when mixed with water. When the solution 

 was removed from the chest it became black ; and on looking 

 into the chest itself it was found to be covered with a black 

 coating of sulphide. Only a conjecture as to the cause of the 

 phenomenon observed can be made. Hyposulphite of soda 

 is an unstable salt, breaking down and freeing sulphur and 

 hydrogen sulphide. Both of these will attack nickel and form 

 nickel sulphide, which may exist in a colloidal state. It may 

 have been the presence of colloidal nickel sulphide which gave 

 the effect observed. When the nickel was not present, as in 

 the former experiment, iron and copper sulphides could have 

 been formed, which might have given the same effect. 



A 60-per-cent. solution of cane-sugar was examined at the 

 temperature 25° and a speed of 37 revolutions per second. 

 The sensibility was '0001 X. No effect was observed. A 

 30-per-cent. solution of cane-sugar was examined at the tem- 

 perature 25° and a speed of 44 revolutions per second. The 

 sensibility was "00003 X. No effect was observed. 



Conclusions. 

 The peculiar behaviour of colloids has led to much con- 

 jecture as to their inner structure. It is convenient to speak 

 of them as forming " a solution "; but in the strict use of the 

 term it is doubtful whether this is true. A substance in 

 solution is understood to be in a molecular condition very 

 similar to a substance occupying the same space in the form 

 of a gas. The laws of Boyle, Avogadro, and Gray-Lussac 

 apply to solutions as well as to gases. Nernst, in his ' Theo- 

 retical Chemistry/ takes these phenomena into consideration, 

 and sees no essential difference in the action of the colloids 

 and crystalloids. He says : — " Formerly it was questioned 

 whether colloid solutions were to be regarded as simple 

 emulsions or as true solutions. But now, since we must 



