in Food.

BY C. M. VORCE, F. R. M. S.

VI. BUTTER.

Butter was for a long time regarded as one of the very few articles that could not be successfully adulterated, as it was supposed that any adulteration would either be perceptible to taste or smell, or else would cause this very perishable product to spoil. But at the present time butter is as extensively adulterated as any other article of food. The first well-known and successful imitation of butter was the now very common oleomargarine, which, however, cannot rightly be

matter. The square crystals of common salt are always present usually in small, but sometimes in quite large crystals, as shown in fig. 3. The clear fluid of butter is saturated with salt, as may be shown by taking up a little butter on a sharp knife-blade and wiping the edge across the slide, or by using the edge of another slide as in spreading a film of blood. The extremely slight smear thus made on the glass, if examined uncovered, by a 1-inch objective, will show a crystalline structure (fig. 4), at first clear and

FIG. 3.-BUtter.

called an adulteration of butter, since there is no butter in it. Still it is popularly classed, with the later product suene, as an adulterated or artificial butter, and as it competes with pure butter in the markets, and is frequently sold as pure butter, we will, for the purpose of this article, consider it among the adulterations of butter.

Pure butter, if fresh and sweet, when examined in a thin film under the microscope, is found to consist entirely of very small globules of oil suspended in a limited amount of clear fluid, chiefly water, associated with a small amount of very fine granular matter with which are occa

FIG. 4.-SALT-CRYSTALS.

transparent, but before long gradually becoming dendritic and opaque, at last showing feathery cystallization as the opacity spreads.

With polariscope and selenite giving a blue field, the polarizing action is faint, but when the field is darkest, a few minute, bright points wil be seen; the crystals of salt are of the color of the field but with black margins.

Only fresh butter should be examined for comparison, for butter that is old develops different crystals of salt, and becomes strongly active upon the polarized ray, owing to the formation of acids. In old butter, we find the field full of branching crystals of salt (fig. 5), and the cubes of salt instead

b

FIG. 5.-SALT-CRYSTALS FROM OLD BUTTER. of being clean cut with smooth edges, are rough and jagged. With the polariscope and selenite, when the field. is red, innumerable spots and blotches of bright blue, many of them of considerable size, will be seen, and extremely minute acicular, colorless crystals, with an increased amount of the granular matter present.

If any adulteration has been effected, it will be detected by its appearance, in addition to the above described characteristics. An excess of brine, or salt, is sometimes purposely added, but unless the excess of brine be considerable it is probably not a wilful adulteration, but the result of imperfect working.

The chief adulteration of butter now practised is undoubtedly the admixture of lard, producing the article called "suene," and sometimes "butterine." This product, when freshly made, is indistinguishable by taste or smell from the best pure butter, and in cold weather it keeps in this condition for a considerable time. Dealers and manufacturers claim to be able to distinguish this from pure butter by the grain," as they call it. The tryer, when withdrawn from a tub of butter, has a "velvety feel" and a peculiar soft look, while from suene it has a "grainy feel" and look, and from oleomargarine a "waxy feel" and 'greasy" appearance, they

Prof. Roger's Micrometers.

BY J. D. COX, F. R. M. S.

It is well known that Prof. William A. Rogers, of Harvard Observatory, has for some years been devoting much time, labor and money to perfecting our means for the accurate and scientific comparison and subdivision of standards of length. A machine made for him at the Waltham Watch Manufactory has been brought, under his tireless efforts, to a degree of perfection which would seem to leave very little to be desired. Results which he has reached in the ruling of micrometer plates, are so far superior to what has been heretofore done, that every one who has occasion for micrometic work must be interested in them, and the scientific world ought not to be slow in proving and recognizing the value of the improvement made.

I have a glass micrometer plate ruled by him about a year ago, containing subdivisions of the inch and the centimetre in the following form: 1st. a band of five hundred lines inch distant from each other. These are finely but rather strongly ruled. 2d. This band is continued across the plate to the right by five hundred more lines of the same spacing, but ruled very lightly and delicately. 3d. Beneath band No. 1, is another of the same spacing ruled very lightly like No. 2. 4th. This last is continued across the plate by one ruled more strongly, like No. 1. 5th. Under No.

3

is a band of five hundred lines, onethousandth of a centimetre apart, strongly ruled, and this is followed by a sixth, seventh and eight band in the same relation to this that Nos. 2, 3 and 4 are to No. I and with alternation of the strong and light ruling.

The whole plate is thus a sort of checker-board of alternating parallelograms strongly and lightly ruled, of which the upper four are subdivisions

of the inch, and the lower four subdivisions of the centimetre, there being four thousand lines ruled on the whole plate within a space four-tenths of an inch long and wide. The lefthand lines of the whole plate are made to coincide, so that a direct comparison may be made under the microscope, not only of the subdivisions of the inch with each other, but of the subdivisions of the inch with those of the centimetre. To facilitate this, the fifth and tenth lines of the inch-divisions are made longer and extend into the centimetre band a little way, so that the gain of the inch-divsions is seen in the regular way in which the fifth and tenth lines cut further into the centimetre spaces, gaining one whole division in 621⁄2.

The first line of the fourth band of the inch divisions being continued downward as above described, is found apparently to coincide with the eighth line of the second band of the centimetre divisions (or the ninth, if the last line of the first band is counted as the first line of the second), and five hundred of the subdivisions of the inch are equal to five hundred and eight of those of the centimetres. In other terms I μ = -in., or the centimetre will be .3937008-in.

Since making the examination of the plate, I am informed by Professor Rogers that the comparative value of the yard and metre which he used in ruling this plate was Kater's, viz. 39 37079. This is the same as the ratio given by Beale ("How to Work with the Microscope") as the English statutory relation. Prof. Rogers has since ruled other plates with the Chisholm ratio, viz.: 39.37112, and is working upon an independent comparison of the English and French official standards.

Taking the Kater ratio which the professor used in making the plate, it will be found by computation that if we divide .2-inch by 507.995 we shall get the centimetre value 3937046; and if we divide the .2

inch by the Kater ratio, 3937079 we shall get the number of spaces 507 990+. It is thus shown that the apparent equality upon the plate of 508 of the centimetre spaces with 500 of the inch-divisions, cannot be out of the way by one-hundredth of one of the divisions; but as these divisions are inch, the maximum difference is one two-hundred and fiftythousandth of an inch. As the space between the striæ of a fine Amphipleura pellucida is a hundred-thousandth of an inch, and the 19th band of Nobert's plates is but little closer, it needs no further proof that the apparent coincidence of the lines described above cannot be distinguished from complete coincidence by any objectives made, and we are unable to prove that Prof. Rogers has not exactly transferred to the plate the ratio between the centimetre and the inch.

Let us now take a general view of the plate itself. If we begin at one end of the bands in juxtaposition and go carefully through it, we cannot fail to be struck with the great evenness of the gain of the inch-divisions upon those of the centimetre. The more accustomed one is to the comparison of micrometer divisions, the more lively will be his surprise and pleasure at finding that in all these five hundred spaces thus compared there is no visible mark of inequality. I have never seen any other ruling which would stand even this test of the direct comparison of such bands of striæ ruled at different times and by a different, though related, scale.

But, of course, the final and only strict test for the microscopist is the actual measurement of the spaces by means of camera, of eye-piece micrometer, or by photography. By means of the Jackson eye-piece micrometer I have made a comparison of this plate with two stage-micrometers of standard European make. Of these one is known by a series of experiments made in the Coast Survey Office, to be made with a screw giv

ing the divisions about two per cent. too large, but the divisions are exceptionally even, as micrometer ruling goes. The other has the average length of the divisions nearly accurate, but they are of inferior evenness.

The power used in examining them was about 450 diameters, as the coarseness of the lines in the ordinary micrometers was such that with greater magnification the liability to error in judging when the hair-line of the eye-piece was in the middle of the stage-micrometer line was more than an offset to the advantages. With Prof. Rogers' plate a higher power could be made useful, because the lines themselves are finer.

The following is the result of a series of average evenness of results out of a number made with each micrometer.

Hundredths of an inch-Plate No. 1.

Space- 1 2 3 4 5 6 7 8 9 Measure 45 44.8 45.2 45.4 45.1 45 45.2 45.4 45.1 10 11 12 13 14 15 16 17 18 19 20 45 45.3 45.5 45 45 45.2 45.4 45.2 45 45.1 45.5

1

2

piece to those on the stage. I thus made twenty divisions of the ocular, equivalent to seven of the plate. Twenty successive tests of this measure applied to twenty different groups of seven spaces each, showed no variation whatever. The value of the thousandth was thus made, -357 throughout.

Next, I examined separately twenty single spaces, each 50-inch, with a higher power (one-tenth objective). These were taken at irregular intervals across the plate, and brought successively to the same line in the eyepiece, the tube being adjusted till the first was as exactly as possible equal to six spaces in the ocular. The plate stood the last test quite as well as before, each division precisely filling the measure applied to it, and being magnified 750 times.

Of course it would not do to say that there are absolutely no inequalities in the spacing, but only that were none measurable by the means employed, and that by whatever means the divisions were measured, their regularity and equality were something unparalleled in my experience.

But

It is true also that the above gives no test of the absolute accord of the divisions with the standard inch or centimetre. For that we must trust Prof. Rogers' methods till some very elaborate tests can be applied. it certainly shows both that the relation of the fractional inch to the centimetre is exactly reproduced in the plate, and that the subdivisions are equal to each other within inappreciable limits.