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mixture of gum and starch, and each of these substances would have to be separately estimated by the methods already described.

For the detection of the tragacanth we are recommended to boil the milk, and leave it at rest for some hours, when a gelatinous translucent deposit will be formed, which, being washed with a small quantity of water and tested with a few drops of solution of iodine, produces a blue colour, because gum tragacanth contains starch. The starch of gum tragacanth is plentiful and is in the form of starch corpuscles; these are rather small, but vary much in size; many are irregular, some are rounded, others are somewhat polygonal, while a few are muller-shaped; in the more perfect grains a rounded hilum is distinctly visible.

On the detection of cerebral matter.-The presence of cerebral matter in milk may be determined with certainty by means of the microscope, portions of the nerve tubules being readily discovered with that instrument, as shown in the engraving (fig. 132).

On the detection of chalk.-If the milk be diluted with water and set aside for some hours, part of the chalk, if present, will have subsided as a precipitate, when it may be sufficiently identified by its

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appearance and its effervescence with acids. Or a portion of the milk may be evaporated to dryness, the residue incinerated, and the chalk estimated from it in the manner pointed out in the articles on · Tea’ and · Water.'

On the detection of carbonate of magnesia.- This has been said to occur only in cream; it would be detected by the insolubility of the ash in water, its effervescence on the addition of an acid, and lastly by the crystalline precipitate which is thrown down from its solution in hydrochloric acid on the addition of a solution containing ammonia, chloride of ammonium, and phosphate of soda.

On the detection of salt. --The saline taste of the ash will show the presence of salt if that substance has been employed. This must be determined from the ash by the process described under “Water.'

On the detection of lead, copper and zinc.-Since milk is not unfrequently contaminated with these metals, the analyst may be called upon to determine whether they are present, and especially zinc, or not. The methods for the detection and estimation of the two former of these metals will be found given under the heads of “Water' and Bread.'

The presence of zinc may be detected in the solution of the ash of the milk in hydrochloric acid by rendering it alkaline with caustic potash, filtering, and adding a few drops of a solution of sulphuretted hydrogen to the filtrate. A white precipitate, consisting of sulphide of zinc, will prove the presence of that metal, and from the weight of the precipitate its amount may be determined. See • Vinegar.'

On the detection of annatto.—The presence of annatto is rendered probable when the milk, evaporated down to a small quantity, presents a reddish or orange-red colour; if this colour is materially altered on the addition of an alkali or an acid to the milk, being rendered purplish by the one and of a brighter red by the other, its presence is certain. Lastly, by means of alcohol, the colouring matter may be dissolved out of the soft residue of the evaporated milk, and the effects of the reagents mentioned tried upon the alcoholic extract.

On the detection of turmeric.—If turmeric has been used in substance to colour milk, it would be possible to detect the turmeric cells. However, it is best to proceed by the method indicated for the discovery of annatto. The chief difference is that the turmeric is rendered deep brown by alkalies.

It is of course rarely, if ever, necessary to examine milk for more than two or three of the articles above enumerated. In general it is sufficient to determine whether water, the ordinary adulteration of milk, has been added or not.

THE DETECTION OF THE ADULTERATIONS OF CREAM. Sufficient has already been said under the heads of the analysis of milk and the detection of its adulterations to enable the analyst to detect and estimate all the known adulterations of cream.

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CHAPTER XIX.

BUTTER AND ITS ADULTERATIONS.

DEFINITION OF ADULTERATIOX.

Any foreign substance, as the fat of beef, mutton, or pork ; flour, starch, or any mineral matter other than salt, which should not exceed 4 per cent. in fresh, and 8 per cent. in salt butter ; curd, which should not exceed 4 per cent. ; and water, which should not be more than 12 per cent.

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As the method of making butter may not be known to many of the readers of this report, we will proceed, before entering upon the consideration of its adulterations, to give a very brief outline of the manner in which butter is usually prepared.

Butter is made for the most part from cream ; the cream is collected from time to time, and placed in a covered jar, until sufficient has been obtained, when, having become sour by keeping, it is submitted to the process of churning.

Butter is also prepared in small quantities from sweet cream, and this kind is esteemed a great delicacy. Very excellent butter is likewise sometimes made from full or entire milk; the disadvantages of this method are—the large quantity of fluid to be acted on by the churn, which renders it necessary that steam or some other powerful mechanical means should be had recourse to, and the length of time which elapses before the butter forms.

As soon as the butter has formed, it is removed from the churn, and well washed in water, it being kneaded at the same time until as much as possible of the adherent and incorporated whey is removed ; this is known by the water ceasing to become turbid and milky. If intended for salt butter, the salt should be added as soon as possible after churning and washing, as, left for any length of time, the butter is apt to become rancid. Great attention should be paid to the quality of the salt used; the best descriptions are rock salt and that prepared from salt springs. Sea salt, generally, is not so good, on account of the presence of sulphate of magnesia, which renders it somewhat bitter, as well as of chloride of calcium, which has a strong affinity for water, even attracting it from the atmosphere.

It would be out of place in this report to enter into the practical minutiæ of butter-making, such as the temperature at which the cream

or milk should be churned, the best kinds of churn, the methods of churning, &c., all points of the greatest importance for the agriculturalist and the dairyman.

COMPOSITION OF BUTTER.

Butter consists of the glycerides of certain fatty acids, principally of stearic, palmitic, and oleic acids, with smaller quantities of butyric, capric, caproic, and caprylic acids ; these latter are all distinguished from the former acids by their volatility. According to the analysis of Bromeis, they amount to only 2 per cent., they being embraced by that chemist in the term “butyroleic acid.' But Messrs. Angell and Hehner have proved, as will be shown hereafter, that these volatile acids are present in much larger quantities, amounting on an average to 9:3 per cent.

The true melting point of butter, taken in the manner described hereafter, we found to range from 32.8 to 34:9, the mean of all the observations made being 33.7° C.

The oily or buttery part exists in milk in the form of innumerable very distinct globules, of various sizes. The effect produced by churning is to break down these globules, which then run together, and thus form butter. The operation of the churn is therefore chiefly, if not entirely, mechanical.

THE ANALYSIS OF BUTTER. The analysis of butter is very nearly the same as that of milk, since it contains for the most part the like constituents, although in very different proportions. It is, therefore, not necessary to enter into any lengthy details on the subject. The water is to be estimated by the loss on evaporation, the fat by extraction with ether; the curd and salt are left on the removal of the fat; the quantity of the former may be estimated by incineration, and the mineral matter remaining may be calculated as salt, of which it usually almost entirely consists.

Butter, when fresh, is of a yellowish colour, having a peculiar and characteristic sweet odour, but when exposed for a long time to the air it loses gradually its colour, becomes white, and acquires a tallowy odour, which was at one time considered to be characteristic of beel, mutton, and other analogous fats; and samples of perfectly genuine butter, when thus changed in colour and odour, have unquestionably in many cases been declared to be adulterated. In fact, by many analysts the tallowy smell was considered to afford a conclusive proof of the adulteration of any butter with some foreign animal fat.

THE OCCURRENCE OF CRYSTALS IN BUTTER. It is very generally believed that the occurrence of needle-like crystals, often arranged in the form of spherules or stellæ, is a cer

scum or

tain proof of the adulteration of butter and of the presence of lard or some other foreign animal fat. This belief, however, is entirely erroneous; and although no crystals are found in freshly-made butter, yet they appear in it if kept for any length of time, and they are especially abundant in all butters which have been fused and allowed again to solidify. On the surface of all such butters a shi pellicle may be seen, composed in large part of such crystals, which are likewise to be found abundantly diffused throughout the whole mass of the butter. Again, they are frequently met with in great numbers in cream. They polarise light. Messrs. Angell and Hehner make the following remarks in reference to crystals in butter :-If a small quantity of a fat containing crystals be placed upon a slide, a drop of castor or olive oil be added, and the whole then pressed out by means of a thin glass cover, the depolarisation of light is much enhanced. A revolving black cross, not unlike that of starch grains, is seen in great perfection. These crosses are most clearly defined in the crystals obtained from butter.

Dr. Campbell Brown, in his essay on the Adulteration of Butter,' remarks :-“A microscopic examination with polarised light is the most reliable means of distinguishing pure butter from that which contains an admixture of less easily digestible and palatable fats. But this statement, as we have seen, is erroneous.

THE ADULTERATIONS OF BUTTER.

Adulteration with water.–One of the most frequent practices had recourse to in the case of butter is to incorporate with it large quantities of water; the incorporation is effected in the following manner: the butter is brought to the melting point, water and salt are then stirred in until the mixture becomes cold.

In reference to the adulteration of butter with water and salt, Professor Calvert, in his evidence before the Parliamentary Committee on Adulteration in 1855, made these remarks: -- The quantity of water and salt that such an article as butter ought to contain is 24 per cent. of salt, and 10 per cent of water. In the butter supplied to these Unions the quantity of salt varied from 2 up to 14 per cent., and the water from 10 to 15 per cent.'

A butter factor wrote to us some time since, stating that 50 per cent. of water may be incorporated with butter in this way; but when you buy, say half a pound of butter, a considerable part of the water of adulteration escapes, and if you put it in paper more will be lost.

Adulteration with starch.—Another adulteration to which butter is occasionally subject, especially the inferior kind known as Bosh, consists in the addition of starch, usually potato flour. This adulteration is practised only at particular times, and is dependent upon the wholesale price of butter.

Adulteration with curd.— Again, butter has been known to be adul