24 



NA TURE 



[May lo, 1877 



Several pieces of pig iron were put into a ladle (holding about 

 one ton of metal) ; these at /irst sank, and a rush of hot metal 

 took place upwards ; after a few seconds the pieces of pig iron 

 appeared /haling, -inth very lilile of their bulk above the 

 surface of the molten metal. A piece of llattish metal of irre- 

 gular shape floated with a small portion alone of its corners 

 above the surface ; it was close to side of ladle. Pieces of flat 

 ca.<-.t-iron bars, 20" X 2" X i", were carefully placed on surface 

 (the latter being well skimmed) ; they floated without going 

 below the surface. One of these pieces, which was put in etui 

 on, kept in this position for a few seconds, with its upper end 

 above the surface ; the other end then came up and floated on 

 its flat side. In some cases a sharp crack was heard when the 

 metals touclied, and a white flame on one occasion burned like 

 a gas jet from the side of one of the pieces. 



The surface of the molten metal was in constant motion due 

 to the currents within its mass, and showed the variegated tex- 

 ture or "break" pecuUar to this condition of the metal. From 

 notes of an experiment which I arranged for, but did not see 

 carried out, I find that a cast-iron ball of about 2j" diameter, 

 when lowered by a fine wire upon a well-skimmed surface of 

 molten cast iron, disappeared completely at first, and then in a 

 few seconds rose and floated with about half an inch diameter 

 of surface exposed ; it was then raised from the metal, when it 

 showed a red glow on the lower part. It was again lowered, but 

 now did not sink, but floated with about twice the surface ex- 

 posed, as on the first experiment. 



Different views are held as to the behaviour of cast iron when 

 passing from the molten to the hot solid state, and finally to the 

 cold (or ordinary temperature) state. 



Some hold that the molten metal, on solidifying, expands like 

 water passing into ice, and that it retains this expansion to such 

 an extent that the col(l colid is specifically lighter than the molten 

 metal. Others hold that no such expansion takes place, and that 

 finally the cold solid is specifically heaviir than the molten metal. 

 A third view is that the molten metal on solidifying expands, 

 and that it then contracts during cooling, until it reaches ordi- 

 nary temperature, when through the cooling it is specifically 

 heavier than in the molten state. 



From the fact that in foundry practice the linear contraction 

 is taken at ,,'5'^ P^f^ there can be little doubt that the finally 

 cooled solid is specifically heavier than the molten metal ; again, 

 fiom the sharpness of form of iron castings and other circum- 

 stances, expansion appears to take place on solidification. 



The above experiments, I think, favour this latter view, as the 

 floating took place more readily with small than with large 

 pieces, partly due to their relative bulks and surfaces. 



A probable explanation, in part at least of these phenomena, 

 I think, is that the cold metal, when at first put in, is specifically 

 heavier than the molten metal, but owing to the great heat around 

 it (over 2,000° F.) it is rapidly heated, and consequently expanded, 

 and when sufficient volume has thus been obtained it floats. It 

 is evident that small pieces, being more readily heated, may re- 

 main floating, whilst heavy pieces, whose volumes are larger in 

 proportion to their surfaces, will take longer to heat, so as to 

 induce the required change of volume, and may therefore at first 

 sink, remaining below the surface till sufliciently expanded to 

 rise and float. The experiment with the ball bears out this well, 

 as, being a sphere, its surface was a minimum. 



These experiments appear to corroborate very well those of 

 your correspondent. 



The following experiments which I lately made with lead may 

 be of interest : — 



An ingot of lead of 14 lbs. weight was placed on the surface 

 of about 160 lbs. of molten lead; it at once melted. After 

 allowing the metal to cool a little, an ingot was carefully placed 

 on the surface, when it immediately sank, bubbles lising up to 

 the surface ; it was heard to strike the bottom of the ladle. 

 Another ingot was tried ; it also s.ank, and could be felt at the 

 bottom (these ingots were cast from the lead in the pot). A 

 small solid piece was cast of about i., lb. weight, which also 

 sank. Pieces of sheet lead were rolled up and placed on surface ; 

 these ytete/; the contained air and great surface in the latter 

 would account for this. 



These latter experiments with lead correspond very well with 

 those of your correspondent with zinc. W. J. MiLLAR 



Glasgow 



Yellow Crocuses 

 In my garden the sparrows do (not touch the crocuses. In 

 that of a friend, some miles off, they attack the yellow ones 



exclusively. I address you chiefly to report a fact related to me 

 by the vicar of a neighbouring parish, whose garden is infested 

 with mice. He tells me that for some time he thought he could 

 not grow crocuses at all, as the mice destroyed the corms, disco- 

 vering and digging down to them, even when there was no trace 

 of the plants on the surface. At last he found that they did not 

 attack the purple crocus, and on his planting the edge of a long 

 border, with alternate clumps of yellow and purple crocuses, the 

 mice almost entirely destroyed all the clumps of yellow, but left 

 the purple untouched. Possibly the purple plant possesses some 

 acrid or bitter taste, rendering it nauseous to animals — the corms 

 to mice, the flowers to sparrows and other birds. 

 Newton-le-Willow.=, May 4 Thomas Comber 



Hog- Wallows and Prairie Mounds 

 If Mr. Williams is right, and the " hog-wallows" are simply 

 American cousins of our "eshars" or "kames," is it not rea- 

 sonable to credit that "atmospheric erosion " to which Prof. Le 

 Conte attributes the formation of the former with a much more 

 important influence upon the shapes of the latter than British 

 geologists generally seem disposed to accord to it? It is very 

 difficult to conceive that mounds of loose sand and gravel, 

 whether in valleys or on plains, should have retained the impress 

 of the glacier or the iceberg throughout the vast time that must 

 have elapsed since these phenomena entirely disappeared. And 

 if it be conceded that these mounds have been modifiei in any 

 degree by subaerial denudation, it will be found diflicult to 

 limit the extent to which they are indebted to it for their present 

 forms, or indeed to deny that it alone may have shaped them. 

 Newport, Fife, May 7 Jas. Durham 



A " Golden Bough " 

 In the gardens of New College, Oxford, there is a fine avenue 

 of horse-chestnut trees, most of which have had some of their 

 lower limbs lopped off, followed by the usual crop of abundant 

 smaller shoots around the original bough. In one tree, how- 

 ever, vrith respect to one severed branch, these resultant shoots 

 bear, year after year, not green, but pale yellow leaves, the 

 summer through — - 



" Primo avulso non deficit alter 

 aureus, et simili frondescit virga metallo." 



It would be interesting to know of other instances of such a 

 veritable "golden bough," and whether any explanation can be 

 given of chlorophyll so remarkably failing to develop its blue- 

 green constituent under no obviously peculiar circumstances. It 

 seems a strange anomaly to find an apparent case of host and 

 saprophyte in one. Henry T. Wharton 



SPONTANEOUS GENERATION 

 /^N Friday evening last the Rev. W. II. Dallinger made an 

 ^^ important communication to the members of the Royal 

 Institution on " Recent Researches into the Origin and Develop- 

 ment of Minute and Lowly Life-forms ; with a Glance at the 

 Bearing of these on the Origin of Bacteria." Biological Science 

 to-day presents us with a magnificent generalisation ; and that 

 whicli lies within it and forms the fibre of its fabric, is the estab- 

 lishment of a continuity — an unbroken chain of unity — running 

 from the base to the apex of the entire organic seiies. But 

 does this imposing continuity find its terminus on the fringe 

 and border of the organic series, and for ever pause there? or, can 

 we see it pushing its way down and onward into the unorganised 

 and the not-living, until all nature is an unbroken sequence and 

 a continuous whole ? That such a sublime continuity may be 

 philosophically hypothecated is to be believed. But that data 

 have been presented to us demonstrating how and by what path 

 the inorganic passes to the vital, the living into the not-living, 

 may be denied. The properties of living matter distinguish it 

 absolutely from all other kinds of things, and the facts to-day in 

 the hands of the biologist furnish us with no link between the 

 living and the not-living. This is an inference which has been 

 fiercely disputed. 



But what are the nature of the proofs relied upon to establish 

 the " spontaneous " or not living origin of living things ? They 

 were chiefly thermal experiments upon the lowest septic 

 organisms, without an attempt to discover what was their life 

 history, and whether they propagated by germs or not. It was 

 argued that the adult organisms being killed at a given tempera- 

 lure much below the boiling point of water, if an infusion were 

 boiled with every possible precaution, and whiLt boiling her- 



