534 REPORT — 1889. 



4. A Note on the Volatilisation of Lead Oxide and its Action ujpon Glass at 

 Loiv Temperatures} By T. W. Hogg. 



The author described a few simple experiments which show that oxide of lead 

 will corrode or attack glass, and also volatilise in small quantities at a temperature 

 of scarcely visihle redness. 



If oxide of lead be used as a pigment to write or mark upon a polished plate of 

 glass, and this is then heated to the above-named temperature for about one hour, 

 upon cooling and brushing off the surplus oxide, there will be found a distinct 

 corrosion or etching upon the surface, due to the oxide having entered into 

 combination with the constituents of the glass; this action will take place even 

 below visible redness, in which case the corroded surface is quite smooth ; if the 

 operation be conducted at a decided red heat the appearance is like that of a dry- 

 hydrofluoric acid etching. 



Very pretty results may be obtained by converting this surface corrosion into 

 sulphide of lead ; this is easily done by soaking the plate in a solution of ammonium 

 sulphide ; brilliant mirror-like films of sulphide of lead may be obtained under certain 

 conditions. 



It has also been found that if a plate of glass be heated to a scarcely visible 

 redness its polish is so extremely sensitive to the slightest trace of lead vapour, that 

 this fact may be made use of to show that lead oxide is slightly volatile also at 

 this temperature. To render this evident it is only necessary to place upon a glass 

 plate or platinum foil some writing, using oxide of lead as a pigment ; if a polished 

 plate of glass be placed over this as closely as possible, and prevented from actual 

 contact by suitable means, upon now heating up to the previously mentioned tem- 

 perature for not less than an hour, a distinct reverse of the design will appear 

 upon the surface of the upper glass ; the quantity of lead oxide which will produce 

 this eSect is not shown by the most delicate balance. 



5. On the Molecular Weights of the Metals : an application of Baoulfs 

 Method to Alloys. By C. T. Heycock, M.A., and P. H. Neville, M.A. 



The authors have made a number of experiments, using sodium, potassium, and 

 especially tin, as solvents, in order to determine the effect produced on the freezing- 

 point of a metal by alloying other metals with it. 



They find that if successive quantities of a metal be dissolved in tin, and the 

 freezing-point observed after each addition, the fall in the temperature of the 

 freezing-point is at fii-st sensibly proportional to the amount of foreign metal added. 

 For strong solutions the effect produced by each addition of metal slowly decreases. 

 It often happens that before any gradual falling oft' in the effect is noticed, the 

 freezing-point becomes constant, no further addition of metal having any effect. 

 This indicates that the tin is saturated with the other metal. The authors think 

 that they have thus determined the exact solubility in tin of silver, copper, and 

 various other metals, at the temperatures at which the respective alloys solidify. 

 These saturated alloys are probably the only ones which can solidify homogene- 

 ously. - 



They find that the effect produced by equal masses of different metals is 

 inversely as their atomic weight — i.e., that 24 grams magnesium produce the same 

 fall as 108 of silver or 196 of gold. 



The fall in the temperature of the freezing-point of the tin when one atomic 

 weight of foreign metal was dissolved in 100 atomic weights of tin was, for most 

 of the metals examined, about 2'6° 0. ; but aluminium produced about half the 

 fall, or 1'2° C, while antimony caused a rise. 



Similar results were got when sodium was used as a solvent, but the corre- 

 sponding fall was about 4° C. ; while a few experiments with potassium as a 

 solvent gave 1'7° C. as the fall for the above concentration. 



' Published in extenso in the Journal of the Society of Chemical Industry, October 

 1889. 



^ These saturated alloys are Guthrie's ' entectic ' alloys. 



