148 



CHEMISTRY. 



thus incorporated must be in the finest state of 

 division. 



To etch the crystalline forms on glass, M. 

 Kuhlmann mixed with a solution of sulphate 

 of magnesia the fluoride of copper or zinc, then 

 exposed the glass plate to sulphydric acid, or 

 dipped it in strong sulphuric acid, in either of 

 which cases fluorine is set free, corroding the 

 glass along the outlines of the crystals. Better 

 still, the plate may be exposed to action of 

 gaseous fluorhydric acid. 



For engraving, or rather raising, the forms 

 on metals, having produced on the surface of 

 an iron or copper plate a crystallogenic design, 

 a surface of lead or copper is then laid over 

 this, and the plates together are submitted to 

 strong pressure ; the design is thus imprinted 

 on the second plate. From the latter a fac- 

 simile of the design in relief is then obtained 

 by the galvanic method; and this is used to 

 print from. M. Kuhlmann believes that in 

 these discoveries he has laid the foundation of 

 a new industry. No account, however, of the 

 adoption of the new methods by manufacturers 

 has been met with. Full accounts of the pro- 

 cesses thus far described will be found in Le 

 Technologiste, Jan., Feb., and April,. 1865. 



The same author has described (Comptes 

 Rendus, Ix. 1115; CJiem. News, August 25, 

 1865), certain interesting transformations of 

 crystals, by keeping them for a sufficient time 

 in solutions of a different nature. Thus, a crys- 

 tal of carbonate of soda, placed in solution of 

 sulphate of copper, gives place ultimately to a 

 true artificial geode, the lining of which (at 

 least) consists of amorphous carbonate of cop- 

 per, the soda-crystal itself having meantime 

 disappeared in the solution. A green and a 

 blue hydrated carbonate thus produced corre- 

 sponded in color respectively with azure stone 

 and malachite, though they contained more 

 water. Beautiful geodes of different colors 

 were obtained by plunging crystals of car- 

 bonate of soda in solutions of sulphate of nickel, 

 nitrate of cobalt, &c. By modifications of the 

 process, other interesting products were se- 

 cured ; as, gold in beautiful crystalline spangles, 

 by placing some of its chloride (contained in a 

 porous vessel) in the midst of a solution of 

 protoxide of iron, of hyposulphite of soda, or 

 of oxalic acid. 



Mineral Arborizations in Solutions of Alka- 

 line Silicates. Filling a glass jar of convenient 

 size with solution of silicate of soda or potash, 

 of the strength (with the former, at least) given 

 by diluting the commercial solution with about 

 five times its volume of water, and dropping in 

 a few crystals of sulphate of copper or iron, a 

 sort of mineral vegetation, of slender stalks and 

 branches, and of the color of the sulphate used 

 olive green with iron, and light blue with 

 copper soon springs up ; and this may, in the 

 course of a few hours, quite fill the jar with 

 delicate arborescent or moss-like forms, similar 

 to those seen in the moss agate. The direction 

 of the stalks and branches depends on the den- 



sity of the solution ; their production appears 

 due to formation of mineral silicates; and the 

 uniformity of direction of the branches in the 

 same solution has been thought to indicate in 

 the latter a sort of invisible cleavage. The two 

 sulphates above named can be used together, 

 and with them also sulphates of nickel and zinc. 

 The illusion is heightened by previously sprink- 

 ling the bottom of the jar with washed sand, 

 adding a little bichromate of potash to give the 

 appearance of soil, and powdered sulphate of 

 copper [or iron] over some parts, to imitate 

 grass. With care, the vessel can be moved; 

 or the silicate solution can, in some cases, even 

 be displaced by a gentle stream of water, after 

 the arborizations are formed. Some remarks 

 on this topic appear in the Jour, of the Frank- 

 lin Institute, June, 1865. 



Efflorescence of Crystals. Dr. Pape (Poggen- 

 dorffs Annalen, No. 2, 1865) finds that this 

 change always commences at certain points, 

 which bear a constant relation to the form of 

 the crystal. This we must suppose to hold true 

 of spontaneous efflorescence only ; since Fara- 

 day found that the point at which efflorescence 

 shall begin can be determined by scratching the 

 surface of a crystal; and this was true with 

 crystals of carbonate, phosphate, and sulphate 

 of soda, which had previously been kept with- 

 out change for years. In a continuation, later, 

 of his investigations, Pape shows that the spon- 

 taneous efflorescence is propagated in spots of 

 determinate form, generally partaking more or 

 less of the ellipsoid, and the proportions of the 

 diameters of which are intimately connected 

 with the form of the crystal. Akin to this ap- 

 pears to be the well-known fact of the differ- 

 ence in the heat-conducting powers of a crystal 

 in the directions of its different axes. Upon 

 newly formed crystals of Glauber's salt, large 

 elliptical spots may be noticed within five or ten 

 minutes after their removal from the mother- 

 liquor. Sharply defined spots in like manner 

 appear, after the lapse of a day or more, on sul- 

 phate of zinc. The most rapid spread is in the 

 direction of the shorter axis of the crystal ; the 

 slow est, in that of the longer. The effl orescence- 

 fignre on any face thus depends on its position 

 with regard to the axes. The author suggests 

 that observation of these figures may be resort- 

 ed to, when the ordinary criteria are unsatis- 

 factory, for determining the system to which a 

 crystal belongs. 



V. THEORETICAL CHEMISTRY. For the most 

 important of the topics requiring notice the 

 present year, and which come appropriately 

 under this head, the reader is referred to the 

 separate articIeTNoMEXOLATUBE AND NOTATION, 

 CHEMICAL. 



Satur ability, as distinct from Equivalency. 

 In an article entitled, " On a Defect in the Theory 

 of Saturation" (Philos. Mag., vol. xxviii.), Mr. 

 E. J. Mills, after citing the facts that the atomi- 

 city or saturability of a given body is expressed 

 by the number of units' weight of hydrogen 

 which can be made to combine with a certain 





