265 



TINCAL. 



TINNING; TIN-PLATE. 



268 



crude method of treating worms to exhibit such a material as tin- 

 filings. [AsTHELMimics.] Even oxide of tin is of doubtful efficacy, 

 as might be expected from its extreme insolubility. Its powers may be 

 heightened by occasionally meeting with acids in the stomach, such as 

 the hydrochloric, and therewith forming a chloride. Two compounds 

 of chlorine with tin are known, one the protochloride, the other the 

 bichloride. Both of these are exceedingly soluble; the latter so 

 much so that it can with difficulty be kept in the solid state, and 

 more frequently occurs in the liquid state, and is then called the 

 spiritus fumans Libavii, or butter of tin. The former is much used 

 by dyers, among whom, when in the solid state, it is called salt of tin, 

 and when liquid, spirit of tin. In the former condition, it has some- 

 times been mistaken for common salt : it has thus been the source of 

 poisoning, though it is not very active when introduced into the 

 stomach. A few grains of it injected into the jugular vein prove 

 rapidly fatal to dogs. In case of any of it being swallowed, emetics or 

 the stomach-pump, demulcent drinks, such as milk, and, if necessary, 

 moderate venesection, may be employed, followed after a time by vital 

 stimulants. A very weak solution of protochloride of tin in distilled 

 water is used as a lotion in chronic cutaneous diseases. It has been 

 thought by some to be dangerous to allow fluids containing acids, such 

 as the weak acid wines, or cyder, or even fatty, saline, or albuminous 

 substances, to remain long in tin-vessels, as an injurious action of these 

 on the tin is supposed to occur. If any serious effects have ever 

 followed from such a cause, it is most likely that these vessels were 

 only coated superficially with tin, which being rubbed off, exposed the 

 more potent metal beneath to the solvent power of these substances. 

 It is, therefore, prudent to examine from time to tune all copper and 

 other vessels to see that the tinning is entire. For small dishes the 

 German enamelled stew-pan is to be commended. 



TINCAL. [BOBACIC ACID.] 



TINCTURES are solutions of the active principles, mostly of 

 vegetables, sometimes of saline medicines, and more rarely of animal 

 matters, in certain solvents. From possessing more or less of colour, 

 they have obtained this name. They are distinguished according to 

 the kind of solvent employed. When alcohol is used, they are termed 

 Jic tinctures, or more generally simply tincturet ; when sulphuric 

 ether is used, they are denominated etfierial tinctures. When wine is 

 used, though differing little from pure alcohol, the term medicated 

 wines is applied to them; and when the process of distillation is 

 employed to aid the extraction, particularly of volatile oils, the result 

 is termed a spirit, such as of rosemary. Ammonia is sometimes con- 

 joined, and the proceeds termed an ammoniated tincture. In some 

 cases less of the principal ingredient is taken up or dissolved when 

 ammonia is used, than when simple alcohol is employed, as in the 

 tinctura guaiaci ammoniata. Formerly some tinctures were called 

 essences, from the term esse, it being thought that they contained only 

 the purer or more refined portion, the alcohol leaving all the baser 

 principles, such as the starch, gum, woody fibre, &c., undi&solved : 

 fence was a still higher degree of this. These terms are now 

 disused by pharmaceutists, though retained in popular language. El'udn 

 differ only from being of a greater consistence : they are not unfre- 

 quently turbid from the extractive matter suspended in them. 

 Tinctures are further distinguished into simple and compound. They 

 are called simple when one substance only is submitted to the solvent ; 

 compound, when two or more are. Another important distinction 

 among tinctures is founded upon the degree of strength of the alcohol 

 employed. Where the active principle is nearly pure resin, a strong 

 spirit is needed ; when much gum is associated with the resin, a 

 weaker is required. Hence some tinctures are prepared with proof 

 spirit, as the greater number; a few with spirit abore proof ; and some 

 with rectified spirit. 



A. well prepared tincture should be clear, possessing the colour of 

 the article which is its base, and partaking in an eminent degree of its 

 characteristic odour and taste. As a general rule, five or six parts of 

 the liquid chosen is to be used for one part of the solid material, which 

 is to be bruised or comminuted before being submitted to maceration. 

 The maceration, which should be conducted in well-stopped glass 

 vessels, is generally continued for fourteen days, during which the 

 ingredients are to be frequently shaken, and at the end strained. The 

 process of displacement by percolation is also good. The pure tincture 

 is then to be preserved in a tightly-stopped bottle, which should be 

 opaque, or sheltered from the light. From several tinctures a deposit 

 falls down, either from some slow chemical change taking place among 

 the ingredients, or from the evaporation of some of the spirit. This 

 renders old tinctures not unfrequently turbid, and of variable strength. 

 Thus tincture of opium when newly prepared contains one grain of 

 opium in nineteen minims, but after some time one grain of opium is 

 contained in only fourteen minims. This inconvenience may be 

 avoided with all recent vegetables, by forming what are termed 

 "vegetable juices." These are merely the juices of the fresh plant 

 expressed by a powerful wooden press, and the juice allowed to stand 

 twenty-four hours, during which a copious precipitation of feculent 

 matter takes place, which is further promoted by adding alcohol 66 

 over proof, in the proportion of four fluid ounces to every sixteen 

 fluid ounces of the juice. After standing for twenty-four hours, the 

 juice is to be filtered through bibulous paper (prepared from wool), 

 when it will keep unimpaired for a length of time. 



These vegetable juices always retain their purity, and are of the 

 same degree of strength at last as at first. By this means not only is 

 the process simplified, and the time required for their preparation 

 greatly abridged, being reduced from fourteen days to two ; but their 

 medicinal efficacy is greater than that of the ordinary tinctures, and, 

 from containing less alcohol, they can be given in cases where the 

 stimulating action of this principle interferes with the effect of the 

 substance dissolved in it, or renders its exhibition improper, as in the 

 case of young children. 



In preparing the officinal spirits, the directions of the Pharmacopoeia 

 are rarely complied with. Most chemists content themselves with 

 dissolving some of the essential oil of the plant in alcohol of the 

 requisite strength, by which much expense and trouble, as well as loss 

 of time, are avoided. 



(See a pamphlet on The Best Method of Obtaining the Most 

 Powerful Vegetable Preparations for Medical Use, by Edward Bent ley ) 



TINNING; TIN-PLATE. The art of tinning, or of coating other 

 metals with a thin layer of tin, so as to protect them from oxidation, 

 was known to the ancients, although it does not appear to have been 

 very extensively practised. During many centuries, England procured 

 tin-plate from Bohemia and Saxony, where the manufactory was esta- 

 blished near the tin-mines of the Erzgebirge mountains, which were the 

 most extensive in Europe after those of Cornwall. From the time of 

 the invention of tin-plate down to the close of the 17th century, if not 

 later, both England and the whole continent of Europe depended upon 

 the above-named countries for their supply of tin-plate ; but about the 

 year 1665 an attempt was made to introduce the manufacture into 

 England. The manufacture was permanently established at.Pontypool 

 in Monmouthshire about the year 1730, and soon afterwards'in France. 

 About 1 7-40 the manufacture was brought to such perfection in England 

 that very little was imported from foreign countries; the British 

 manufacture was superior to the foreign in glossiness of surface, owing to 

 the plates being drawn under a rolling-mill, instead of being hammered, 

 as was common in those made beyond sea. The difficulty of extending 

 iron, in what may be deemed the infancy of the manufacture, into thin 

 uniform sheets, with a perfectly smooth and clean surface, which is 

 essential to the adhesion of the tin in an equal film, was one of the 

 principal obstacles to the progress of this department of the art of 

 tinning. 



The process of tinning depends upon the strong affinity which exists 

 between tin and the metals to which it is applied. The tinning of 

 sheet-iron, as the most important application of the process, will be 

 first noticed. The finest English or Welsh bar-iron, prepared with 

 charcoal instead of mineral coke, and known to the trade as tin-iron, is 

 used for making tin-plates. This material is first made into flat bars, 

 or slabs, about 30 inches long, 6 inches wide, and weighing eighty 

 pounds. These bars are mads red-hot, and extended by passing them 

 repeatedly between rollers, until they are reduced to about 3-8ths of an 

 inch in thickness. When cooled, the pieces are cut by shears, worked 

 by machinery, into plates about 10 inches by 6, which are repeatedly 

 re-heated and rolled, until they are reduced to as thin a state as the 

 process will conveniently allow. The sheet is then doubled and again 

 rolled until reduced in thickness one-half, after which it is doubled 

 again, and rolled until still further diminished in thickness. When 

 thus brought to the required tenuity, the thin sheet is cut into plates 

 of the sizes required to suit the market (most commonly about 1 3 

 inches by 10), and then the several thicknesses or lamina) are separated. 

 After shearing, the plates are piled in heaps, one being laid cross-wise 

 at intervals, to separate the number required to form a box. This 

 name is technically applied to 225 plates in all the subsequent pro- 

 cesses, although it is not until they are completed that the plates 

 are actually placed in boxes. 



The next operation to be performed is the removal of every particle 

 of oxide or other impurity from the surface of the plates. For this 

 purpose each is steeped for a few minutes in a leaden trough con- 

 taining a weak solution of muriatic acid. The plates are taken out, 

 arranged on the floor in rows, and then removed, by means of an iron 

 rod, to a reverberatory furnace or oven, in which they are submitted 

 to a red heat. The heat to which the plates are exposed, combined 

 with their previous washing in the acid, causes them to throw off a 

 scale of rust or oxide. The plates are then flattened by beating them 

 upon a cast-iron block, and are submitted to a second or cold rolling, 

 which removes any warping acquired in the previous processes, gives a 

 high degree of smoothness to their surfaces, and imparts elasticity to 

 the iron. After the cold rolling the plates are immersed singly, in a 

 vertical position, in an acidulous preparation consisting of water in 

 which bran has been steeped for nine or ten days, until it has fermented 

 and become slightly acid. In this the plates are kept for ten or twelve 

 hours, and occasionally turned, to insure an equal exposure of every 

 part of then- surface ; and from the lye-trough they are transferred to 

 a leaden vessel containing diluted sulphuric acid. This trough and the 

 lye-trough are slightly heated by flues, to assist the action of the acid 

 menstrua. The plates are usually agitated in the weak sulphuric acid 

 for about an hour, until they become bright and free from black spots, 

 They are then removed into pure water, in which they are scoured 

 with hemp and sand, to remove any remaining oxide ; and in this bath 

 of pure water the plates remain until wanted for tinning ; because, 

 even if left for mouths, they will remain perfectly free from rust. 



