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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Jan. 6, 



sence of carbonate of lime. In all cases, where we take common soil and 

 see efTervcscence. it may be attributed to carbonate of lime. 



The chemist goes from this to ascertain what quantity of carbonate of lime 

 tliere may be in any soil which he may think it right to examine, and this is 

 a simple operation. The following is the process:— Put into the pan of a 

 balance, two flasks, one containing a previously weighed quantity of the soil, 

 the other some muriatic acid, and counterpoise them. Then pour some of the 

 ,ncid on to the soil, so long as efl'ervescence takes place from the escape of 

 carbonic acid, which will, of course, leave that pan so much lighter. The 

 weights which are requisite to be added to the pan containing the flasks to 

 restore the equilibrium, will give the weight of carbonic acid that has es- 

 caped ; and then, by adding 28 paits (for the limej to every 22 parts of loss, 

 you will ascertain the weight of the carbonate of lime originally present. (Oi-, 

 what will do equally well, multiply the loss by 2'2727 ) 



There are a number of foreign matters occasionally associated with car- 

 bonate of lime, which were once entirely overlooked. These foreign matters 

 are now frequenlly considered of greai importance ; whether they are of that 

 immense importance which some seem to attach to them, is a matter for future 

 experience to determine. True it is, however, that there are in limestones 

 certain bituminous substances, as well as potassa, soda, magnesia, phosphate 

 of lime, &c. Upon this latter, very great stress has been laid, and it has 

 been considered a very important ingredient of the soil, especially in lime- 

 stones, It is found in limestones certainly in very minute quantities, form- 

 ing less than one per cent., but it must be remembered that if the soil contain 

 only one grain in a pound of foreign matter, that when you multiply i t by the 

 quantiiy of soil in an acre of ground, it soon mounts up amazingly, so that 

 the smallest quantity may be a matter of the utmost importance. The chalk 

 about Brighton, upon being examined by Elirenberg with a microscope, was 

 found to consist of a multitude of animalcuh-E. This led us to look at phos- 

 phate of lime, which is always found associated with corals and relics of that 

 kind as important. No doubt such chalk would form a very vaUnble 

 manure, if we may allow the term, to chalk which does not contain phos- 

 phate of lime. We now now come to an important subject — the con- 

 verting of limestone into lime— that is, how to get rid of the carbonic 

 acid. And first, as to the characteristics of carbonic acid. If you collect 

 it in the form of gas, as I have done, you will find it a very heavy gas, and 

 it extinguishes flame. An instance of its weight may be seen by decanting a 

 vessel of it into one containing atmospheric air, when you will find that it 

 will displace the atmosiilieric air at the bottom of the jar. For this reason 

 it collects in pits and wells, w here it is known under the name of the choke 

 damp. It is extraordinary, that if a person descends into a well containing 

 it, he will be immediately suffocated ; but if it is diluted to a certain extent 

 he can then breathe it, and it acts as a narcotic poison— drowsiness comes on 

 rapidly and he dies. But there are a number of gases which extinguish flame . 

 we must not rest satisfied therefore that carbonic acid is the gas, unless you 

 have this other test by lime water, which it will convert into carbonate of 

 lime. 



1 have said, that carbonic acid and lime have but little affinity for each 

 other ; and now to get rid of the carbonic acid. You have seen that the acid 

 drives it ofli' by effervescence. But the common mode of getting rid of it 

 consists in burning the limestone. It you lake a quantity of chalk, suppose 

 50 cft't., and expose it in a proper kiln to tlie action of a proper heal, you 

 will find that 22 cwt. goes off in the shape of carbonic acid, and Ihit 2H cw t. 

 remains, and this which remains is lime, known under the name of caustic or 

 quick lime. 



I will not go into the question of burning lime, but it is a very important 

 one. It should be burnt in a current of air, and if damp, so much the belter. 

 You may take a piece of chalk, and put it into a close vessel and keep it hot 

 for days, and yet not get rid of the carbonic acid ; so that you see tlie aflinity 

 between carbonic acid and lime is not so feeble after all : but w hen you expose 

 it to a current of air and moisture, their joint operation carries away the 

 carbonic acid, and thus you may in a short time entirely divest the carbonate 

 ul lime of its acid, Mow 1 nearly remeniLer ihe time when it was thought 

 that when you burnt lime the limestone absorbed the fire, and that that was 

 the reason why lime was so hot. Now, we know, in consequence of Dr. 

 Black's discoveries, that tlie mildness of chalk is owing to the prseence of 

 carbonic acid, and that the heat of lime is the consequence of its expulsion. 



Lime is possessed of many important properties which fit it for agricultural 

 ]iurposes. One of which is, the changes it undergoes upon being exposed to 

 the air. If you expose quicklime to the action of the air, it gradually crumbles 

 down into a powder. In doing this it absorbs water from the atmosplierc. 

 and it also absorbs carbonic acid, so that lime, after being exposed to the air 

 for a week is no longer quick lime, but part of it has become chalk, and part 

 hydrate of lime, i.e. lime in conncxii^n with water. The strong aflinity which 

 lime has lor water makes chemists sometimes use it as a means of drying air. 

 This strong affinity is best illustrated in the operation of slaking lime— that is, 

 throwing water upon it. Here we have two kinds of lime, one contains a 

 quantity of aluminous earth, the other is pure lime. If we pour water upon 

 these, we shall find that the temperature begins to.nse enormously, and that 



is a proof that chemical combination is taking place; and this occurs much 

 more rapidly in what is termed " fat lime," than in " meagre lime." A great 

 deal of heat is evolved in the operation— often enough to set fire to sulphur 

 or matches. The lime then crumbles into a fine white i>owder, and this pow- 

 der is slaked lime. Every 28 parts of lime combine with 9 of water; so that 

 37 parts of slaked lime are equivalent to 28 of quick or caustic lime. 



Now having slaked the lime, if you expose it to the air it gradually absorbs 

 carbonic acid, it parts with water, and ultimately passes back to the state of 

 chalk. If to slaked lime you add excess of water, you will obtain a solution 

 of lime called " lime water." About 700 parts of water are required to dis- 

 solve 1 part of lime ; and from this you may obtain a notion of the strong 

 alkaline power of lime, for this solution, ihough it contains only 1 part of 

 lime in 700 of water, has a nauseous bitter taste, and by applying the common 

 tests, it will be founil to be a powerful alkali. No.v if you expose this to the 

 air it will become turbid, as lime water does if added to carbonic acid. 



Carbonic acid is derived from various sources, amongst others from our 

 lungs, and if I blow into lime water, you will see that the air from my lungs 

 precipitates the carbonate of lime. Or if you take some air from a candle, 

 you will find that that is pure carbonic acid. So if we go to a brewer's vat 

 and collect Ihe gas escaping in fermentation, fhat is carbonic acid. If you 

 burn charcoal and oxygen you obtain carbonic acid. If you burn dung in 

 oxygen you obtain carbonic acid. If you burn plumbago, or black lead, you 

 get carbonic acid — that, therefore, is another carbon. If I take some spring 

 water, and test it by lime water, I shall find carbonic acid there— it becomes 

 turbid. In Thames water there is an immense quantity of carbonic acid. I 

 do not point these out as so many isolated facts, having no particular bearing, 

 for they have all their agricultural uses. Waters, in many instances, are im- 

 portant as containing carbonic acid, for water readily permeates the soil, and 

 finds it way to the roots of plants. Air also contains a little carbonic acid, in 

 the proportion of about I in 1000. 



As regards the uses of lime, it may be stated, first, that its alkaline pro- 

 perty makes it a powerful destroyer of worms. If mixed with dead leaves or 

 turf it tends gradually to decompose them, and converts them into mould. 

 Another property is, that it neutralizes acids. Another and most important 

 property is, that it decomposes the salts of iron. Water containing a salt of 

 iron dees a vast deal of mischief to the soil it permeates. This will be cor- 

 rected by lime. If to ferruginous water slaked lime be added, you will see it 

 decompose, the iron is precipitated, anil haf become oxide of iron. Lime 

 also decomposes aluminous compounds. It has also an important action 

 upon animal matter. If a little quick lime be mi.xed with almost any animal 

 matter, ammonia will be the result. If bone dust be added to quick lime, am- 

 monia will be produced : there is, however, no ammonia in bone, and none in 

 lirne, but there are the elements of ammonia in bone. Another effect is that 

 after ammonia has been formed, if there be certain substances in the soil the 

 ammonia passes into nitric acid ; and if it contains potass or soda, nitrate of 

 potass or nitrate of soda is formed. It is probable that the lighter soils of 

 India and America derive their fertility from ammonia. Here the elements 

 of ammonia, mixed with air, produce nitrate of ammonia. 



Felspar mixed with lime, and exposed to the action of water and air, re- 

 acts, and potass becomes evolved with a certain portion of silica. In this 

 state it is thought particularly favourable to the growth of grasses and wheat, 

 width require silica in connexion with potass. With regard to the general 

 tests for lime, the one most commonly used by chemists is oxalic acid. There 

 are other tests, but this is the best. If you take a precipitate of oxalate of 

 lime and heat it, you can convert it into carbonate of lime ; and thus you 

 can come at the quantity of lime in any soil. 



When lime has passed again into a state of chalk, it becomes a valuable 

 ingredient in the soil. It is the same as broken limestone of another kind, 

 but it has this advantage, that it crumbles down into an impalpable powder ; 

 and ihough you may mix ground limestone with the soil, it is never so 

 efiective as when it has been reduced from the state ot quick lime to car- 

 bonate of lime by slaking, when it comes much more readily into contact 

 wilh the roots of vegetables. 



I will not go into this subject now, but I may say that roots of plants 

 appear to be capable of secreting certain acids. 



There are peculiarities derived from the presence of magnesia in certain 

 limestones. M hen it exists in limestone, which is burnt into lime; such lime will 

 remain caustic, and resist the action of the air and water for a long time. If 

 mixed, therefore, with the soil, it will be found to retain its causticity long 

 alter the common lime has become inert. The presence of magnesia may 

 be ascertained by applying nitric acid, which will not dissolve the magnesia. 

 Some limestones contain argil, or clay ; others, oxide of iron, and they 

 derive certain peculiar properties from tlie presence of ihose substances. 



The other salts of lime which claim the agriculturists atleniion, are the 

 sulphate and phosphate of lime, of Hhich 1 shall speak in the next lecture. 



