TRANSACTIONS OF THE SECTIONS. 57 
hydrogen being disengaged, and very shortly the aluminium assumed a fine white 
frosted appearance. The solution of caustic potash, when concentrated, acts very 
violently upon the aluminium; and if the metal were not speedily rescued, it would 
soon entirely disappear. Even a dilute potash solution at a blood-heat will slowly 
produce the frosted appearance. 
The author suggests that the process now indicated may be found of service in the 
arts. Aluminium has hitherto proved itself to be unacceptable on account of its 
similarity in appearance to zinc, but now a frosted surface may be communicated to 
articles made of aluminium, which rivals that of frosted silver, and which possesses 
this great advantage over silver, that it is not liable to be acted upon by sulphuretted 
hydrogen, such as silver is, but continues to retain its fine white frosted appearance. 
On the Combustibility and other Properties of the Rarer Metals. 
By J. A. Marruiessen, Ph.D. FCS, 
The author gave a description of the very beautiful metals obtained from the alkalies 
and alkaline earths, which was illustrated by the exhibition of a variety of these metals, 
as attractive as unusual. The specimens of sodium, lithium, potassium, calcium, 
strontium, &c., were regarded with great interest, and their combustion in an intensely 
brilliant white light elicited frequent expressions of admiration. Their extreme 
lightness was dwelt on, lithium being lighter than any liquid, and possessing little 
more than half the specific gravity of water. From magnesium the combustion ree 
sulted in an ash hollow throughout. 
On Chromatie Photographs. By Joun Mercer, F.R.S. 
The author exhibited a number of coloured photographs, some on paper and others 
on calico, which had been prepared by the following process :—34 ozs. of sulphate of 
iron are converted into peroxalate ; this is diluted to two gallons, and will impregnate 
200 square yards of paper, the paper being floated on the solution till fully wet in 
the usual way. It is then exposed, and afterwards steeped in some solution which 
only acts on that part where the iron has been reduced from the per- to the prot-oxide. 
Red prussiate of potash and sulphuric acid act well, making the image blue, and 
- leaving the ground white, Sulphocyanide of potassium and a salt of copper form 
another bath ; the protoxide of the picture deoxidizes the copper, and the sulphocyanide 
of the suboxide of copper is fixed in the paper or cambric. This may be converted 
into the red copper prussiate. A vast number of colours may be obtained by re- 
placing the iron or copper by other metals, such as lead, zinc, tin, mercury, silver, 
gold, or manganese. With these bases may be used various dyes, as madder, co- 
chineal, murexide, logwood, galls, or quercitron bark, besides the iodides, chromates, 
prussiates, or oxides of the metals themselves and mixtures of these. 
The author showed how the peroxalate paper might be used as a fair actinometer, 
by placing a slip between the leaves of a book, and pulling it out by steps every 
stated number of seconds, It is then easily converted into a graduated scale. 
On the Relation of the Atomic Weights of the Families of the Elements. 
By Joun Mercer, F.RS. 
It is well known that where threc or more elements form a well-defined group or 
family (such as lithium, sodium, and potassium), their atomic weights are found to 
stand in some simple relation to one another. ‘The present paper pointed out many 
of these numerical relations, and those which arise when the equivalents of one group 
are subtracted from the equivalents of another group. Thus, for example, the lithium 
group may be supposed to be constructed in a similar manner to the group of organic 
radicals, hydrogen, methyl, ethyl, &c., as shown in the subjoined Table, where 6=1, 
Lithium = L at.wt. 7 corresponding to H 
Sodium., = 8, L, a 23 a » Hy 
Potassium = 0, L, # 39 3 C, H; 
Thus also, for example, if the atomic weights of the nitrogen group be subtracted 
from those of the fluorine group, the residue is in each case 5. 
