Chemistry and Physics. 333 



running a solution of arsenous oxide in acid potassium tartrate 

 into hydrogen sulphide water, the other (/?) by similarly treating 

 a solution of arsenous oxide in caustic soda. Both these solutions 

 have a clear yellow color by transmitted light and are strongly 

 fluorescent. The /3 solution keeps rather better, depositing only 

 a trifling precipitate in a year. On microscopic examination, 

 solution a was barely resolved with 1000 diameters, solution /5 

 not at all. By diffusion, it was observed that the tartrate in 

 solution a carried out the arsenic particles by its own diffusion. 

 Using Graham's method for solution /?, the solution, contained in 

 a wide-mouthed bottle, being placed in a large beaker and covered 

 with water, it was found that after 32 days there was no sign of 

 diffusion ; the water remaining colorless and containing no arsenic. 

 Evidently the whole of the sulphide is in a state of suspension. 

 Antimony hydrosulphide solution has a fine orange-red color, 

 only slightly fluorescent. No particles could be detected by the 

 microscope at first, but after dialyzing for ten days they appeared, 

 the whole of the sulphide being precipitated when the dialysis 

 became complete; showing a progressive condensation. No dif- 

 fusion was observed into a tartrate solution, but when a calcium 

 light beam was sent through the antimony solution, as in Tyn- 

 dall's experiment, the track of the beam was marked by a beau- 

 tiful soft red glow, the light of which was completely polarized. 

 Hence the solution has no true fluorescence, but consists of 

 exceedingly minute particles in suspension. No filtration of the 

 solution took place through a porous cell, nor did its coagulation 

 develop heat. A third arsenic solution y was then prepared, 

 from an aqueous solution of arsenous oxide. It resembles the 

 other arsenic solutions, but is stronger containing 11 or 12 grams 

 of sulphide in a liter. Only a mere trace of precipitate occurred 

 in four months. Under the microscope no particles could be 

 detected, but distinct diffusion was observed. The beam of light 

 gave a soft yellow glow completely polarized. The author con- 

 cludes that " there seems to be no satisfactory reason for imagin- 

 ing the existence of any sharp boundary between solution and 

 pseudo-solution. It is quite possible that the one merges by 

 imperceptible gradations into the others." — J. Chem. Soc, lxi, 

 137, February, 1892. G. f. b. 



5. On Solution and Pseudo-solution. — Continuing the above 

 i*esearches, Picton and Linder have studied the character of a 

 variety of colloidal solutions. The solutions of mercury, anti- 

 mony and arsenic hydrosulphides already examined present a 

 series passing from matter in a state of subdivision not too fine 

 to allow of its observation under the microscope, to particles so 

 fine as to diffuse after the manner of ordinary solutions. Indeed 

 arsenic a is made up of particles just visible under the micro- 

 scope, arsenic /? contains no visible particles, while arsenic y con- 

 sists of particles so minute as to be diffusible. Mercuric sulphide 

 dissolves in hydrogen sulphide water, and the vibrating particles 

 are readily seen under the microscope. This state of pseudo-solu- 



