heated on the water bath until all smell of chlorine has disappeared. A current of pure sulphuretted hydrogen is now passed through the liquid for at least twelve hours, it being heated to about 70° C. at the same time. The arsenic, if any be present, is thereby precipitated in the form of sulphide of arsenic, mixed with a large quantity of sulphur and organic matter. The precipitate is collected on a filter, washed with water containing some sulphuretted hydrogen in solution, and dried. The filter with the precipitate is then drenched first with pure strong nitric acid and then with sulphuric acid, and heated on the sand-bath in a small porcelain basin until fumes of sulphuric acid begin to escape. The mass is then allowed to cool, and the arsenic extracted with water acidulated with pure hydrochloric acid. Sulphuretted hydrogen is again passed through the liquid, whereby the arsenic, together with any heavy metal which may be present, is thrown down in the form of sulphides, this time in a state of purity. If the precipitate be of a pure yellow colour and soluble in a solution of carbonate of ammonia, there cannot be any doubt of the presence of arsenic; but if it be black, as would be the case if copper be present, it must be washed with water containing sulphuretted hydrogen and then extracted, with yellow sulphide of ammonium. The arsenic passes into solution, whilst the sulphide of copper remains undissolved. The liquid is filtered and the filtrate is acidulated with hydrochloric acid, whereby the sulphide of arsenic is again rendered insoluble. The precipitate of sulphide of arsenic is collected on a filter, dissolved in ammonia, and the solution again precipitated with hydrochloric acid. Thus the sulphide of arsenic is obtained in a pure state.

For its further identification it may be mixed with dry cyanide of potassium and carbonate of soda, and heated in a slow current of carbonic acid, when pure arsenic will sublime.

If the metallic arsenic thus obtained be heated with access of air by breaking off the closed end of the tube, arsenious acid will be formed, which sublimes and crystallises in the cool part of the tube in the form of well-defined octahedral crystals, plainly visible with a lens or a low power of the microscope.

CHAPTER XXI.

LARD AND ITS ADULTERATIONS.

DEFINITION OF ADULTERATION,

Any foreign substance, whether animal, vegetable, or mineral; as dripping, farina or flour, alum, &c., excepting water and salt, which should not exceed two per cent. respectively.

LARD is the fat of the pig freed from the tissues in which the fatty matter is contained. The process by which this is separated from the vesicular, fibrous, and vascular tissues in which it is either enclosed, or by which it is surrounded, is termed lard rending.

The pieces of fat to be converted into lard are sometimes salted a little, the better to ensure their preservation, and are stored in barrels. The fat which immediately surrounds the kidneys yields the best and purest lard; this is owing to its being in a freer state, that is, it is less highly organised. The process is as follows:-The pieces of fat are scored or sliced into lesser portions of an inch or so in diameter; they are placed, either with or without the addition of a little water, in cauldrons, which are usually of iron. The mode of applying heat to the flare varies in different cases. When lard is made on a small scale the flame is often applied directly to the containing vessel; sometimes the flare is melted in a water-bath, but usually the heating medium is steam, which is contained in the interval between the inner and outer vessel or pan; occasionally a jet of steam is thrown directly upon the flare contained in the copper. The oily part of the fat melts out and floats on the surface, the animal matter and tissues either forming a scum, which is skimmed from time to time, or sinking as a deposit. As the oil has no affinity for either water or salt, it does not take up any of the water which may be present with it in the copper, while the salt used to preserve the fat is partly held in solution and partly falls as a sediment. The oil, whilst still warm and fluid, is turned out of the copper through a tap, and is received either into bladders or casks termed kegs, and hence the division of lard into bladder lard and keg lard. It is usually the best description of lard only which is stored in bladders, keg lard being for the most part of inferior quality. Good and pure lard should be entirely free from either taste or smell; it should be firm and white, and when melted be almost as clear and transparent as water; subjected to a tempera

ture of about 100° C., it should liquefy without ebullition, thus showing the absence of water, and should not throw down a particle of deposit. Inferior or adulterated lards possess characters and properties almost the reverse of these. The melting point of lard, as determined by the author with considerable care, ranges from 42.6 to 44.6, the mean of several observations being 43.6° C. According to Braconnet its composition is as follows:-Stearin and margarin, 38; olein, 62.

Our supplies of lard are derived principally from Ireland, part also comes from America and Hamburg, while London and our chief provincial cities possess lard manufactories.

THE ADULTERATIONS OF LARD.

We have long been aware that lard, like nearly every other article of consumption, is liable to adulteration: indeed, the fact that it is so is very generally known to dealers, as also the nature of the principal adulterations practised.

The chief adulterations of lard resemble those of butter, and consist in the incorporation with it of water and starch. Sometimes the water only or the starch only is had recourse to; in others both these adulterations are practised on the same lard.

We have ourselves met with many samples of lard adulterated with potato flour; but one of the earliest to draw attention to the subject was Mr. George Whipple, in a communication which he brought before the Pharmaceutical Society, and which was noticed in its Journal for January 1853; in this he states that he had detected large quantities of some farinaceous substance in lard.

'This adulteration,' writes Mr. Whipple, was discovered in the different varieties of lard-from the finest bladder to the common firkin lard. In an examination of the contents of two firkins, weighing 105 lbs., a quantity of farinaceous substance, amounting to 22 lbs., was separated. The contents of another firkin, weighing 43 lbs., yielded 123 lbs. of a similar substance.'

In the next number of the same journal, Mr. Calvert, of Manchester, published some further observations on the adulteration of American lard. He writes:During the numerous analyses I made some three years since of various articles of food employed in public establishments, I analysed several samples of American lard, and therefore may add to the fact already mentioned by Mr. George Whipple in your last number, that I found them to contain, in addition to starch, from 10 to 12 per cent. of water, and from 2 to 3 per cent. of alum, and about 1 per cent. of quicklime.

'A few months ago I was able to ascertain that the operation is conducted in the following manner :—

The fatty matters, such as they arrive from America, are melted with a little water in false-bottomed copper pans, through which circulates a current of steam. The dirt and other heterogeneous matters

fall to the bottom of the pans, and the clear grease is allowed to run into a wooden vessel, when it is stirred in contact with cold water; it is then put under revolving wheels with a thick paste made of potato starch, mixed with a little potash alum and quicklime, which appears to facilitate the taking up of the water and starch by the fatty matter. 'The cause of the American lard appearing so white is, no doubt, the division of the fatty matter through the interposition of the starch, water, and alumina.

'The quantity of alum should be such that a small excess should remain to prevent the starch from becoming mildewed; and I believe that the manufacturer also adds it for the purpose of communicating to the lard the property of facilitating the raising and increasing the whiteness of the confectioners' paste, in which it is largely employed.'

It should be understood that American lard, as brought to this country, is not in general adulterated. The adulteration usually takes place subsequent to its arrival, and is the work of some of our own manufacturers. The reason why American lard is so frequently selected for adulteration is, that it is of inferior quality and value, and so soft as to be almost fluid, some process of consolidation being indispensable before it can be employed as lard.

From information received from a respectable lard-render, it appears that the addition of a small quantity of mutton suet to lard is very common. It is used more particularly in warm weather, and with soft lards, especially American lard, which differs from ordinary lard, in that it consists of the entire fat of the pig melted down, and not, as is the case with the best English lard, of the fat only which surrounds the kidneys. Mutton suet, being a hard and firm fat, imparts to soft lards, even when added in very small quantities, the consistence and solidity requisite.

It appears, therefore, that water, starch, alum, and caustic lime have all been ascertained to be employed in the adulteration of lard. To these substances we may add the following:-Carbonate of soda, carbonate of potash, and salt. The whole of the above adulterations may be readily discovered.

Results of the Examination of Samples.

The results of the examination of upwards of 100 samples of lard were as follow:

1. That lard is not unfrequently extensively adulterated, the ingredients employed being water and potato flour, as well as certain saline substances, as salt, potash alum, carbonates of potash and of soda, and caustic lime, these being intended either to cause the lard to hold water, or to improve its consistence and colour.

2. That the description of lard most liable to adulteration is keg lard, and of this, particularly that which is manufactured in England; Irish keg lard being but rarely adulterated.

3. That of upwards of one hundred samples of lard submitted to examination, and procured chiefly from retail dealers, seven were found to be adulterated with potato starch.

The adulteration of lard prevails not only in certain localities, but also chiefly at certain times-that is, whenever a sufficient supply of inferior lard, suitable for mixing, can be procured; for it is said not to answer to adulterate a lard of good quality, which commands a high price, and which is spoiled by being tampered with.

It will be readily perceived that the qualities of a lard thus adulterated must be seriously impaired for almost every purpose for which it is employed: thus, of course, it would not be nearly so economical for culinary purposes. The use of such lard in machinery might, in some cases, produce serious consequences by impeding its action. Lastly, the activity of all the ointments of the Pharmacopoeia, made with such a lard, would be much injured, especially the simple and compound iodine ointments, which, if starch were present, would, to the astonishment of the dispenser, turn blue, or almost black, in the act of incorporation.

The Detection of the Adulterations of Lard.

The first thing to be done in order to ascertain whether a lard be genuine or adulterated, is to melt it at about a temperature of 100° C. If it fuse without ebullition or without the occurrence of a deposit, we may safely conclude that the sample is genuine; but if ebullition take place, or a sediment is thrown down, the lard is unquestionably adulterated.

Detection of water.-The adulteration of water, and the quantity present, may be thus determined:-A known weight of lard, say 2 grammes, is to be exposed to heat until the lard ceases to lose weight; the loss indicates the quantity of water.

Detection of starch.-The presence of starch may be discovered by thoroughly mixing a drop of a tincture of iodine with a few grains of the lard, placed upon a slip of glass; the lard will change colour, and become deep blue, or almost black. If now a little of this be viewed under the microscope, the starch corpuscles will themselves be seen coloured by the iodine.

To determine the kind of starch contained in any sample, we must use the microscope. A minute piece of the lard should be placed on a glass slide, previously thoroughly warmed; the moment the lard is melted it must be viewed by the object glass, when the starch corpuscles will be distinguished standing out as clearly as though they were in water.

Another way in which the starch corpuscles may be well seen by the microscope, is to spread out by gentle pressure, between two pieces of glass, a very thin stratum of the lard, or the fatty matter may be first removed by means of ether and the residue examined.