CHEMISTRY. 



101 



enumerating these colors I do not refer to inter- 

 ference colors produced superficially by reagents 

 also wonderfully brilliant but to body colors. 

 As a single instance of coloration, the following 

 may be mentioned : I recently obtained a solu- 

 tion of allotropic silver of an intense yellow- 

 brown. A little solution of disodic phosphate 

 changed this to bright scarlet (like Biberich 

 scarlet), presently decolorizing with formation 

 of a purple precipitate. Washed on a filter, this 

 changed to bluish green. The colors I have met 

 with in this investigation can only be compared 

 with the coal-tar products, of which one is con- 

 stantly reminded by their vividness and intense 

 calorific power." 



A joint discussion by the chemical and phys- 

 ical sections of the British Association on the 

 nature of solution and its connection with os- 

 motic pressure, was opened by Prof. Pickering 

 in a paper on the present position of the hydrate 

 theory of solution. The supporters of the hy- 

 drate theory claim that the curved figures, rep- 

 resenting the properties of solutions of various 

 strengths, show sudden changes of curvature at 

 certain points, which are the same whatever be 

 the property examined, which correspond to the 

 composition of definite hydrates, and which, 

 therefore, can only be explained by the presence 

 of these hydrates in the solutions; while the 

 supporters of the physical theory, now identified 

 with the supporters of the osmotic-pressure 

 theory, claim ,to have shown that, with weak 

 solutions at any rate, the dissolved substance 

 obeys all the laws which are applicable to gases, 

 and that therefore its molecules must be unin- 

 fluenced by. and uncombined with, those of the 

 solvent. With regard to the lowering of the 

 freezing point of a solvent, the following ques- 

 tions were proposed : 1. Is the molecular depres- 

 sion (or that produced as calculated for, 1 mole- 

 cule dissolved in 100 molecules) constant inde- 

 pendent of the nature of the solvent ? 2. Is it 

 independent of the strength of the solution so 

 long as this strength does not exceed the limits 

 (gas strength) above mentioned (Boyle's law)? 

 3. Is it independent of the nature of the dissolved 

 substance (Avogadro's law) ? Evidence was ad- 

 duced involving a negative answer to each of 

 these questions. Objection was taken to the 

 theory of dissociation into ions, on the ground 

 of its irreconcilability with our ideas of the rela- 

 tive stability of various bodies and with the 

 principle of the conservation of energy. 



While experimenting on the action of strong 

 light on phosphorus, Prof. A. Pedler has reached 

 the conclusion that the term " amorphous phos- 

 phorus " is a distinct misnomer, and that com- 

 mercial " amorphous " phosphorus is really the 

 same substance as the form called rhombohedral 

 or metallic phosphorus. The slight differences 

 in character noticed between the substances in 

 question are explained by the difference in the 

 state of division and the slight variations condi- 

 tioned by their mode of formation. Whether 

 the term amorphous phosphorus can be truly 

 applied to the forms made by the action of light 

 is open to doubt. Even in this case there ap- 

 pears to be distinct evidence of crystalline form, 

 although, in some instances, a form which ap- 

 peared to be amorphous was obtained. The dis- 

 use of the term is suggested. The author finds 



that when phosphorus is exposed to light in 

 contact with liquids containing oxygen, such as 

 alcohol, it tends to enter into action with them. 

 He further describes experiments which tend to 

 show that red phosphorus is not permanent in 

 air, as is commonly supposed. 



The British Association Committee for the 

 investigation of the action of light on the hy- 

 dracids of the halogens in presence of oxygen 

 have found that the presence of 10 per cent, of 

 hydrochloric acid prevents all decomposition of 

 chlorine water, even after long exposure to sun- 

 shine. Aqueous solutions of pure bromine and 

 iodine have been exposed to sunlight for a pe- 

 riod of fourteen months. It was found that in 

 a dilute solution of bromine water, as much as 

 57 per cent, of the total bromide is converted 

 into hydrogen bromide ; in a saturated solution, 

 the minimum amount of decomposition occurs, 

 but increase follows further additions of bromine. 

 With iodine water under an atmosphere of car- 

 bon dioxide, 8'3 per cent, of the total iodine in 

 the solution was converted into hydrogen iodide. 

 Under an atmosphere of air 14'2 per cent, of the 

 total iodine was converted. Further experi- 

 ments have been made on the oxidation of 

 gaseous hydrogen bromide in sunlight. The 

 presence of free bromine exercises a retarding 

 influence on the decomposition. The influence 

 of temperature on the oxidation of hydrogen 

 chloride and bromide has been studied. Rise of 

 temperature appears to retard oxidation in the 

 first case and accelerate it in the second. 



Reactions which can be started or accelerated 

 by sunlight may be expected to be more active 

 when the rays are concentrated by a concave 

 mirror. Herr Briihl verified this in the produc- 

 tion of zinc ethyl from zinc and ethyl iodide, 

 when the reaction, usually difficult to start, was 

 vigorous and complete. A lens would be less ef- 

 fective, since glass obstructs the passage of heat. 



The experiments of Prof. H. B. Dixon and 

 J. A. Harker on the rates of explosion of hydro- 

 gen and chlorine in the dry and wet states 

 showed that there was no such great difference 

 in the rate as had previously been found by the 

 authors with carbonic-oxide and oxygen mixt- 

 ures. It thus appeared that in the cases of these 

 substances, the aqueous vapor acts like any other 

 inert gas, making the rate a little slower. 



Dr. G. S. Turpin has begun a thorough inves- 

 tigation of the conditions affecting the ignition 

 of explosive mixtures of gases. A paper read by 

 him in the British Association relates to the 

 temperatures of ignition of various mixtures of 

 carbon-disulphide vapor with oxygen and other 

 gases. A discontinuity between gradual com- 

 bustion and ignition proper is found to exist in 

 some cases, while in others there is a perfect 

 gradation from slow combination, attended by 

 a faint glow, to instantaneous combination, at- 

 tended by a bright flame. The effect of change 

 of pressure on the ignition was examined and 

 found to be somewhat complex. 



Concerning the action of water at high tem- 

 peratures and great pressures upon wood and 

 cellulose, H. Tauss finds that pure cellulose gives 

 traces of sugar at the ordinary pressure. At 

 higher pressures the quantity of sugar increases, 

 but at twenty atmospheres it is converted into 

 hydrocellulose. Wood is attacked by water at 



