Lists of incompatibles are published in many pharmaceutical and medical works, but are, in reality, of little use beyond illustrating rules and principles which are familiar to every chemist, and which every prescriber should also be intimately acquainted with.
INCRUSTATION, Prevention of, in Steam Boilers. With all qualities of water commonly used for feeding steam boilers there is a tendency to the production of hard calcareous deposits or layers of incrustation within the boilers, due to the separation of lime salts (particularly the carbonate and sulphate, or mixtures of these with a certain amount of carbonate of magnesia) as the direct consequence of the accumulation of these impurities from large quantities of water evaporated. The sparing solubility of the sulphate of lime (gypsum) in hot water fully accounts for its deposition in the boiler, and the carbonate of lime (chalk) is thrown down, not only as the result of direct evaporation, but by the ebullition expelling free carbonic acid, which holds this body to some extent in solution. Rain water, which of itself is too pure to give rise to these incrustations, cannot be used alone for boiler purposes, for it has been found to exert a highly corrosive action upon the iron plates and fittings. It can, however, be advantageously employed in conjunction with ‘hard’ spring or river waters, and has the effect of diminishing the incrustation merely as the result of dilution. The drain pipes leading from the roof of the factory may be placed in connection with the tank or well from which the supply of water is drawn for the boilers. It will be seen hereafter that the self-same remedy is efficient both as a means of preventing incrustation and obviating corrosion, and that by using one of the alkaline substances about to be specified this twofold advantage may be secured. Iron will not rust when immersed in water containing a mere trace of caustic alkali, and it is a common observation that the iron vessels used in the preparation of potash and soda remain for any length of time free from all appearance of rust. This singular property is, no doubt, susceptible of important applications, amongst them may be mentioned the better protection of iron ships from the attack of bilge water, of hydraulic rams, moulding boxes, smith’s tools, and other objects liable to be placed at times under the influence of water. Some forms of surface condensers become quickly corroded in consequence of the purity of the water accumulating in them by the process of distillation, and a small dose of caustic alkali is then useful as a means of protection; the engine-cylinders also to some extent are preserved when alkaline anti-incrustation fluids are introduced into the boilers, for the minute quantity which is carried forward mechanically in the form of spray mixed with the steam, suffices to preserve the iron. Whilst a tendency to ‘priming’ undoubtedly results from a too liberal use of soda or other alkali in the boiler, it will in practice be found easy to adjust the proportion of this ingredient, so as to secure immunity from corrosion and incrustation, and at the same time, avoid the tumultuous kind of ebullition known as ‘priming.’ In all cases it is advisable to carry out a rigid system of inspection, and it is only in the way of saving fuel and labour that the application of boiler fluids is to be recommended.
Much benefit has often resulted from a coating of coal-tar or ‘dead oil’ applied to the interior surfaces below the water line, when the boiler is opened for cleaning and inspection. These will tend very considerably to lessen the adhesion of calcareous crusts, and are not in any way affected by the boiler fluids in common use. Soda crystals and caustic soda may be used with great success in boilers to effect the immediate precipitation of the lime salts, and they act by throwing down a finely divided form of carbonate of lime, which in time furnishes nuclei for the deposition of subsequent accretions both of the carbonate and sulphate, so that they are prevented from crystallising upon the walls of the boiler. A granular mud is thus formed, which subsides quickly and may be for the most part got rid of through the ‘blow-off cock,’ which should be opened for this purpose two or three times every day, and run out with as little water as possible.
The use of caustic soda has undergone a thorough trial at the hands of Mr J. Spiller, F.C.S., in the boilers of the Royal Arsenal,
Woolwich, and we are favoured with the following general instructions regarding its use, which are based upon an experience of upwards of ten years. The caustic soda should be dissolved in water so as to make a concentrated solution of specific gravity 1·300. This, being perfectly miscible with water, may be introduced into the boiler with the feed-water at any time when, from the pressure of steam, it may not be convenient to pour it through the safety valve or other openings in the boiler. But when the steam is down there is no difficulty in introducing the prescribed dose by using a tin funnel with flattened aperture to pass it through the safety valve; or a tubular arrangement with double cocks will answer at all times. Half a gallon per diem is the average quantity found sufficient for a 20-horse stationary boiler, working with Thames water for ten hours daily. If the water should happen to be unusually hard a larger dose may be employed, but it would not be expedient to add in one charge more than the amount required for the day’s consumption. Locomotive and multitubular boilers have been worked successfully with caustic soda, and it is here that the importance of using anti-incrustation fluids makes itself most apparent.
Many other methods have at various times been proposed to prevent the formation of deposits in steam boilers. Dr Ritterband’s method consists in simply throwing a little sal ammoniac into the boiler, by which carbonate of ammonia is formed, which passes off with the steam, and chloride of calcium, which remains in solution. In Holland this plan has been used with satisfaction for locomotive boilers. About 2 oz. of the salt may be placed in the boiler twice a week. The chloride of tin is equal to sal ammoniac, and is similar in its action. Carbonate of soda has been recommended by Kuhlmann and Fresenius of Germany, and by Crace Calvert of England. It is now employed generally in the boilers of engines in Manchester. The common plan adopted by working engineers to prevent incrustations from either variety of water is, on each occasion of cleaning out the boiler, to introduce some substance which, by its mechanical action, shall prevent the precipitated earthy matter caking together, or adhering to the boiler plates. Some common tar, bitumen, or pitch, appears to answer well under most circumstances. Mr Ira Hill recommends the use of 3 or 4 shovelfuls of course sawdust. He states that, after adopting the use of this article, he never had any difficulty from lime, although using water strongly impregnated with it, and has always found the inside of his boilers as smooth as if just oiled. Mr De Haen recommends the sulphate and bicarbonate of calcium to be decomposed by adding barium chloride and milk of lime in the proper proportion; when the water is at a temperature of 35°-45° C. the whole becomes clear in about ten minutes, a precipitate consisting of a mixture of barium sulphate and calcium carbonate deposits; if the water be cold, the greater part separates in ten minutes, but a little turbidity is noticeable for some hours due to suspended matter.
Protzen recommends the introduction of a piece of zinc into the boiler, this determines a galvanic current, which protects the iron against oxidation and corrosion, and causes the mineral ingredients of the water to be deposited as a fine loose mud, entirely preventing the formation of incrustation.
Slippery elm bark, and spent bark from the tan works have also been suggested. We (A. J. Cooley) have worked a powerful boiler daily for months without opening the ‘man-hole,’ after throwing a few pounds of potatoes into it. In all cases, when the earthy matter can be kept in a state of solution, or precipitated in a pulverulent form, it is easily removed from the boiler by what engineers term ‘priming,’ which is allowing the hot water to be blown over with the steam, so that, after a sufficient time, the whole original contents of the boiler are removed, and replaced by fresh water. Before doing so, however, it is of consequence to cut off the communication with the cylinders, and to open the waste-steam cock. Consult a pamphlet on ‘Boiler Incrustation and Corrosion’ by F. J. Rowan, published by Spon, London.
INCUBA′TION (Artificial). The hatching of eggs by artificial heat. This has been practised by the Egyptians from a very remote period. M. Bonnemain has the honour of having introduced this art to Western Europe, in 1775, and having been the first to pursue it successfully on the commercial scale. The source of heat employed by him was a circulatory hot-water apparatus, and the temperature maintained by it 100° Fahr. His plan was to introduce, daily, 1-20th only of the eggs the apparatus was capable of receiving, so that on the 21st day the first chickens were hatched, and a like number every day afterwards as long as the supply of eggs was kept up. Among the trays containing the eggs he placed saucers of water, to compensate for the absence of moisture derived in natural incubation by transpiration from the body of the hen. The chickens, as soon as hatched, were transferred to a ‘nursery’ or ‘chick-room,’ also artificially heated, and were fed with crushed millet seed. Several attempts have been made of late years to introduce artificial incubation into this country, with variable success.
IN′CUBUS. See Nightmare.