14 



NATURE 



[November 3, 1892 



iv., 398). It is stated that the Earl of Powys possesses an 

 onyx containing the chrysalis of a moth. 



It seems to be generally assumed, without any strong 

 evidence, that rock-crystal and agate have been formed 

 from solution in water, possibly superheated, and that 

 in such cases as those mentioned above, various crystal- 

 line or fibrous minerals and low forms of plant life have 

 been inclosed during the process of solidification. 



Though this explanation is very possibly true in many 

 cases, it does not account for all the appearances seen in 

 moss-agates ; and another possible mode of formation 

 iidy be suggested by a brief account of some experiments 

 made more than twenty years ago. 



Ordinary crystals of ferrous sulphate dissolve readily 

 in cold water ; but if they are placed in a dilute solution 

 of an alkaline silicate, an entirely new series of phenomena 

 are produced, which were first described by J. D. Heaton, 

 M.D., in a paper " On certain Simulations of Vegetable 

 Growths by Mineral Substances" (Brit. Assoc. Report, 

 1867, p. 83). On immersing crystals of ferrous sulphate 

 in a solution of sodium silicate of the density 1065, very 

 beautiful arborizations will soon begin to shoot perpen- 

 dicularly upwards, attaining the height of three or four 

 inches in a few hours. In a weaker solution roots can 

 be caused to shoot downwards from a suspended crystal. 

 The fibres contain silica and iron (less the weaker the 

 solution) ; they are brittle, and more dense than the liquid 

 in which they are formed. Examined by the microscope, 

 the ultimate ramifications are cylindrical, tapering tubes, 

 the walls of which are granular, showing no sign of crys- 

 tallization. The roots are more abrupt and occasionally 

 club-shaped in their terminations. The growth is inter- 

 stitial like that of organized living tissue. " Supposing 

 such purely mineral substances to have been formed in 

 by-gone geological eras, and to have been accidentally 

 fossilized in some primary or other ancient rock, they 

 would very probably, when discovered by recent investi- 

 gation, be pronounced to be an evidence of organized 

 beings having existed contemporaneously with the forma- 

 tion of such rock." 



In the following year a similar observation was made 

 by Prof. W. C. Roberts-Austen (J. C. S., 1868, xxi., 274). 

 A solution containing 49 per cent, of silica, when 

 allowed to gelatinize, and dried for two days over sul- 

 phuric acid, left a solid residue similar to opal from 

 Zimapan, but containing 21-4 per cent, of water. All the 

 specimens of jelly dried in air contained dendritic forms, 

 varying in size from 0-2 to 05 mm. When magnified 

 90 times they appeared as radiating fibres ; when the 

 power was increased to 700 times linear, each fibre re- 

 solved itself into a series of elongated beaded cells with 

 clusters of circular cells at intervals. Mr. Slack indicated 

 their remarkable analogy to common blue mould or 

 mildew. The cells appeared to be hollow, and did not 

 blacken with sulphuric acid. 



A few years later I repeated Dr. Heaton's experiments, 

 and made some additional ones, a brief account of which 

 may induce some one with better means at his disposal 

 to mvestigate an interesting and somewhat neglected 

 subject. 



If a crystal of copper sulphate be suspended in a solu- 

 tion of potassium silicate, which has been carefully 

 neutralized and has a density of i '065, in the course of 

 a few minutes a hollow green column will be seen to run 

 down from the crystal to the bottom of the beaker. 

 Sodium silicate may be used instead of potassium sili- 

 cate, but the appearance and rapidity of the growth is 

 somewhat changed. The solution may be neutralized 

 with hydrogen sulphate, chloride, or acetate, but hydrogen 

 fluoride appears to prevent all growth. If the solution 

 has a density less than i"o6, no growth occurs, and the 

 crystals generally dissolve ; the weaker the solution down 

 to this hmit the more rapid the growth. If the solution 

 be stronger, the time required for the growth to com- 



NO. I20[, VOL. 4.7] 



mence may be lengthened from minutes to many days. 

 If the density be above i'25, no growth takes place. 



Copper sulphate gives the best results, but it may be 

 replaced by ferrous, manganous, or nickel sulphate ; with 

 changes in the shape, and of course in the colour, of the 

 growths. The growths take place most readily from a 

 clean sharp crystal, and always from an angle or edge ; 

 an edge obtained by cleavage requires more time. Other 

 salts besides the sulphates may be used, but do not act 

 so rapidly, probably owing to less perfect crystallization 

 of the specimens used. 



In a neutral or very feebly alkaline solution the growths 

 are comparatively rapid, and consist of long, branching^ 

 tapering fibres, not unlike the roots of a tree. They 

 grow rather more rapidly downwards than upwards. If 

 the solutions be decidedly alkaline, the growths are much 

 slower, and consist of fine stalks with comparatively large 

 lumps at the extremities. 



The tubes seem to be composed of silica with a small 

 proportion of the metal used ; they differ much in colour, 

 are more dense than the liquid in which they grow, and 

 are insoluble in water or dilute acids. When magnified 

 100 times, the substance of the tube shows no appearance 

 of crystalline form, but seems to consist of concretions 

 of ovoid granules. In this particular it differs from the 

 substance of lead or silver trees, and from the curious 

 fibres of potassium, iodide, and chloride described by 

 Mr. Warington (J. C. S., v., 136, viii., 31). 



It is generally assumed that the formation of onyx is 

 due to the successive deposition of layers of silica 

 coloured by different substances, but the following ex- 

 periment suggests another possible method of formation^ 

 especially when the extreme permeability of gelatinous 

 silica by liquids is remembered. So readily are even 

 the hardest agates permeated by hot aqueous solutions 

 of salts, that "staining" is a common commercial 

 process. 



A little too much sulphuric acid was accidentally added 

 to a moderately strong solution of potassium silicate in 

 which some crystals of copper sulphate were lying. The 

 copper sulphate dissolved, and the solution set to a. 

 uniform blue jelly. After standing for about a week, the 

 blue colour at the top of the jelly had separated into a 

 series of thin parallel coloured plates, leaving the jelly 

 between them colourless. This curious separation of the 

 colouring-matter gradually proceeded downwards, and 

 reached the bottom of the precipitating glass in about a 

 month. The jelly gradually shrank, dried, and hardened, 

 forming fragments consisting of blue bands in a white 

 mass. Sydney Lupton. 



NOTES. 



There will be a memorial celebration for A. W. von Hof- 

 mann on November 12, arranged by the Deutsche Chemische 

 Gesellschaft,at Berlin on the 25th anniversary of its foundation. 

 The Empress Frederick and many German and foreign cele- 

 brities have been invited to be present. The proceedings, which 

 will take place at the Berlin Town Hall, will include speeches 

 on the history of the Society and on Hofmann, a review of pro- 

 gress in chemical science by Hr. Wislicenus, and choral music, 

 performed by the members of the cathedral choir. 



We regret to have to record the death of Mr. Robert Grant, 

 F.R.S., Professor of Practical Astronomy at the University of 

 Glasgow. He died at Grantown-on-Spey, his native place, at 

 the age of seventy-eight. 



The death of Dr. Lowenherz, director of the Imperial 

 Physical Institute, Berlin, has been announced. He died at 

 Berlin on Sunday last. 



Prof, Virchow^ has been appointed an honorary member 

 of the Imperial Russian Natural Philosophy Society. 



