184.9.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



3-11 



the cool head and ready resources in danger which practice and confidpnce, 

 the result of practice, alone can give. A naval cadet may li-arn navigation, 

 —may know how to steer, to reef and furl, and even to rit? a ship, hy in- 

 structions on shore; hut he would make a sorry seaman without he gained 

 bis experience amongst the rough realities of liis profession. So, also, a 

 civil engineer or an architect may learn how to excavate, to build, and to 

 design at college; hut he must not he entrusted to expend money for others 

 upon his designs, without being qualified by steady, bard practice. 



But we do profess to give the architectural and engineering student that 

 scientific knowledge, that theoretical acquaintance with their business, that 

 when they enter the office of a practical man, they may understand v\hat 

 they see — and understanding, profit by tiie experience they will gain on 

 works entrusted to their charge. From my experience with young begin- 

 ners, it is my decided and serious opinion that they should, before entering 

 an office, learn well all the theoretical branches of their proftssiou, because 

 when in the office they will he left principally to their ovvu resources; and, 

 unless they learn themselves from opportunities offering (not pointed out to 

 them), they may leave the office at the end of their term with probably some 

 knowledge of simple business routine — with some vague and undigested ideas 

 of the conduct of works; but further than that, as little qualified to practice 

 as when they left school. 



In this respect, then, as offering a sound mathematical and scientific edu- 

 cation to yuung professional men, this College ought to be encouraged by 

 the older societies of Civil Engineers and Architerts,— for by doing so, they 

 would receive into their ranks far different, far better, men than they have 

 been in the habit of receiving. 



I earnestly hope, having the dignify of my profession at heart, I may he 

 enabled to unite my strength with tliat of the other professors of this estab- 

 lishment, so effectually, that it may become all that its most ardent support- 

 ers can desire. 



BRITISH ASSOCIATION. 



Nineteenth Meeting, — held at Birmingham, September, 1 849. 



(Continued from page 314.) 



Chemical Section. — Db. Percy in the Chair. 



1. Chi the Decomposition and Partial Solution of Minerals, Kochs, 

 SfC, by Pure Water, and Water charged with Carbonic Acid. By 

 Prof. W. B. Rogers and Prof. R. E. Rogers, of the University of 

 Virginia, U.S. 



In opening this communication, Prof. W. B. Rogers adverted to 

 its important bearings upon the Chemistry of Geology and the 

 tlieories of the formation of soils and of the nutrition of plants. 

 He referred to the experiments of Struve, Forchliammer and 

 others, as being of too restricted a sco|)e to permit a basis for 

 reasoning generally on the disintegration of rocks, the formation 

 of chalcedonic, zeolitic and other minerals by solution, and the 

 conveyance of inorganic materials into the structure of plants. 

 It therefore becomes a question of importance v\hether water, 

 pure or charged with carbonic acid, possesses tliat general decom- 

 posing and dissolving power which some chemists have vaguely 

 and witliout sufficient evidence ascribed to it, or whether this 

 action applies only to the few materials hitherto tried, and which 

 all contain an alkali. 



The experiments of the Professors Rogers wei"e of two kinds: 

 first, by an extemporaneous method with tlie tache, and second, by 

 prolonged digestion, at the ordinary temperature. In the former a 

 small quantity of the mineral in very fine powder is digested for a 

 few moments on a small filter of purified paper, and a single clear 

 drop of the liquid received on a platinum slip is dried and ex- 

 amined by appropriate tests before .Tnd after ignition. In the 

 second process a quantity of the finely-powdered mineral is placed 

 with the liquid in a green glass bottle, and agitated from time to 

 time for a prescribed period. The liquid separated by filtration is 

 evaporated to dryness in a platinum capsule. The residuum is 

 then critically examined, and, if in sufficient amount, is submitted 

 to quantitative analysis. In both processes two parallel experi- 

 ments were made, the one with pure atirated water, the other with 

 water charged to saturation at 60° viith carbonic acid. In the 

 second process correction was made for the alkali, lime, &c., dis- 

 solved from the containing glass, by making separate experiments 

 in similar vessels without the mineral powders. 



1. AVhen the substance is very minutely po^idered before 

 mingling it with the liquid, even the first drops that pass the 

 filter will commonly give a tache containing some of the alkali or 

 alkaline earth that has bren dissolved. In this way proof of the 

 action of the carbonated water may generally be obtained in a few 

 minutes after adding it to the powder. In the case of pure water 

 the action is feebler and requires a longer time; but with nearly 



all the substances enumerated it is distinct, and with some of 

 them quite intense. 



2. By an independent series of experiments, to determine the 

 effect of heat, which were made upon the taches of potassa and 

 soda, and their carbonates, and upon those of carbonate of lime 

 and magnesia, as well as upon considerable quantities of these 

 substances successively exposed in a crucible to the heat of a table 

 blow-pipe, it was found that the order of volatility was as follows: 

 potassa, soda, magnesia, lime. The tache of potassa disappeared 

 almost at once, that of soda lingered some time, that of magnesia 

 wasted more slowly, while that of lime remained with little altera- 

 tion for a long time. Before heat was applied the tache of the 

 alkalies or their carbonates would of course be strongly alkaline. 

 That of the carbonate of magnesia also presented a decided and 

 sometimes strong reaction with the test paper, while that of car- 

 bonate of lime gave a merely appreciable effect. But on raising 

 the tache to a red heat, the carbonate of lime, by escape of car- 

 bonic acid, would acquire intense alkalinity, the reaction of the 

 magnesia tache would be but little altered, and that of the alkaline 

 taches would be almost or entirely destroyed. As examples of this 

 distinctive testing and of the mode of proceeding in these tache 

 experiments. Prof. Rogers gave some details extracted from the 

 large mass of unpublished results, and called attention particu- 

 larly to the contrasting phenomena in the cases of Leucite, 

 Olivine, and Epidote: the first characterised by potassa, the second 

 by magnesia; and the last by lime. Thus, in the case of Leucite, 

 the water tache and carbonic acid water tache were both alkaline, 

 the latter very strongly so. But even gentle ignition for a few 

 seconds, or strong ignition for a moment, was found entirely to dis- 

 sipate the alkali. In the case of Olivine, the water tache was 

 decidedly alkaline; and that from carbonic acid water greatly 

 more so. Ignition produced for the first second or two but little 

 change; but its continuance caused a gradual diminution of the 

 alkaline reaction, which at the end of ten seconds was reduced to 

 about one-twelfth of what it was at first. With Epidote, the tache 

 presented an extremely feeble reaction before heating. Ignited 

 for a moment, the alkalinity was intense; and after ten seconds of 

 ignition, but little abatement of the alkaline reaction was discerned. 



3. Referring to the second method of experimenting used by the 

 Professors Rogers — viz., that of prolonged digestion in water or car- 

 bonic acid water. Prof. Rogers exhibited results obtained with 

 hornblende, epidote, chlorite, mesotype, &c., showing that the 

 amount of solid matter dissipated by the carbonated water in 

 many of these cases is quite sufficient for a qualitative analysis even 

 when the digestion has only been continued for forty-eight hours. 

 When farther prolonged, they have procured from the liquid a 

 quantity of lime, magnesia, oxide of iron, alumina, silica, and 

 alkali, the dissolved ingredients of these minerals severally 

 amounting sometimes to nearly one per cent, of the whole mass. 



4. In connection with the preceding investigations. Profs. Rogers 

 were led to an examination of the comparative solubility of carbonate 

 of lime and carbonate of magnesia in carbonated water. In the 

 standard chemical and geological works, the carbonate of lime is 

 stated to be the more soluble; and on this supposed fact is founded 

 a common theory of the origin of the large quantities of carbonate 

 of magnesia in the magnesian limestones. It was conceived that 

 in a mixed limestone containing both the carbonates, the relative 

 amount of carbonate of magnesia would be augmented through the 

 more rapid removal of the carbonate of lime by the percolating 

 waters, and that thus the mass would approach more and more to 

 the composition of a dolomite. The experiments of the Profs. 

 Rogers demonstrate that in water impregnated with carbonic acid, 

 carbonate of magnesia is much more soluble than carbonate of 

 lime. Thus by allowing the slightly-carbonated water to filter 

 through a mass of magnesian limestone in fine powder, and col- 

 lecting the clear liquid, analysis detected a much larger proportion 

 of carbonate of magnesia in the solution in comparison with the 

 carbonate of lime than corresponded with the amount of those 

 substances relatively in the powdered rock. Again, by agitating 

 briskly a quantity of the powder with the carbonated water in a 

 glass vessel, and then separating the liquid by filtration, it was 

 found that a larger relative amount of the carbonate of magnesia 

 had been taken up by the solvent, than of carbonate of lime. 

 From these experiments, the Profs. Rogers infer that the unfilter- 

 ing rain-water, with its slight charge of carbonic acid, in passing 

 through or between strata of magnesian limestone will remove the 

 carbonate of magnesia more rapidly than the carbonate of lime; 

 and that thus the rock will gradually become relatively less mag- 

 nesian, instead of being made to approach the contiition of a 

 dolomite, as is commonly maintained. Prof, Rogers called atten- 

 tion to the fact that the stalactites in caverns of magnesian lime- 



