1. _Cements._--1. _Brunswick Black._ Boil together 1/4 lb. foreign asphaltum and 4-1/4 oz. of linseed oil (previously thickened with litharge), then mix to a proper consistence with oil of turpentine (about 1 pint).
2. _Gold Size._ Boil 25 parts of linseed oil with 1 of minium and 1/3rd part of umber for 3 hours; pour off the clear fluid, and mix with equal parts of powdered white lead, and yellow ochre, added in small successive portions. Then boil well the whole again, and pour off the clear fluid. It dries slowly, but firmly. Both this and the last are dissolved by turpentine.
3. _Goadby's Marine Glue._ Dissolve separately in coal naphtha equal parts of shell-lac and india rubber. Mix thoroughly with heat.
4. _Sealing-wax Varnish._ Dissolve the best sealing-wax in enough strong spirit of wine to reduce it to the proper consistence. This is brittle.
5. _Canada Balsam._ This dries spontaneously.
Solutions of shell-lac, gum, and various other cements and glues are employed by microscopic manipulators.
_Preservative Fluids._ Canada balsam, spirit and water, glycerin, solution of gelatin, saturated solution of alum, chloride of zinc, and chloride of calcium, are all used to preserve microscopic objects.
The following formulae will be found useful:--
1. _Goadby's Solution._ Bay salt, 4 oz.; alum, 2 oz.; corrosive sublimate, 4 gr.; boiling water, 4 pints. Mix and filter. It may often be more diluted.
2. _Thwaite's Fluid._ Mix spirit of wine, 1 oz., with creosote sufficient to saturate it; rub up with chalk to form a thin paste, and mix gradually with 16 oz. of water. To this may be added an equal quantity of water, saturated with camphor.
3. _Simple Creosote Solution._ Dissolve creosote, 1 dr., in pyroligneous acid, 1 dr., and mix gradually with cold water, 1 pint.
4. _Passini's Solution. For blood-globules, nerves, and white tissues generally._ Perchloride of mercury, 1 part; chloride of sodium, 2 parts; glycerin, 13 parts; distilled water, 113 parts.
=MIL'DEW.= _Syn._ RUST, BLIGHT. The mouldy appearance on the leaves of plants produced by innumerable microscopic fungi. The hop, wheat, and the choicest garden fruit trees, are those most commonly attacked. The causes are said to be excess of moisture, and absence of the free circulation of air and sunshine. On the small scale, finely powered sulphur is occasionally dusted over the parts affected, as a remedy.
=MIL'IARY FEVER.= _Syn._ MILIARIA, L. Among the other symptoms are--anxiety and frequent sighing, the perspiration has a strong and peculiar smell, and there is a sensation of pricking on the neck and breast, followed by an eruption of small red pimples, which in two or three days become white vesicles, dry up, peel off, and are succeeded by others. The moist weather of spring and autumn are the periods in which it is most prevalent; and delicate females, particularly in child-bed, are those most liable to its attacks. Sometimes it assumes a malignant character. The _treatment_ of this affection consists chiefly in combating the depression of the system by a supporting diet; but everything that heats or stimulates the skin should be avoided. The apartment should be kept cool and well ventilated, and cooling saline laxatives and bitter tonics, with cooling drinks, should also be had recourse to.
=MILK.= _Syn._ LAC, L. The value of milk as an article of food is clearly shown by the fact of it being sufficient to support, and to increase the growth of, the young of every species of the mammalia; at once supplying materials for the formation of the osseous, fleshy, and liquid portions of the body. "The substances present in milk are wonderfully adapted to its office of producing materials for the rapid growth and development of the animal frame. It contains an azotised matter, casein, nearly identical in composition with muscular flesh, fatty principles, and a peculiar sugar, and, lastly, various salts, among which may be mentioned phosphate of lime, held in complete solution in a slightly alkaline liquid.
"The white and almost opaque, appearance of milk is an optical illusion.
Examined by a microscope of even moderate power, it is seen to consist of a perfectly transparent fluid, in which float about numbers of minute transparent globules; these consist of fat surrounded by an albuminous envelope, which can be broken mechanically, as in the churning, or dissolved by the chemical action of caustic potassa, after which, by agitating the milk with ether, the fat can be dissolved." (Fownes.)
_Comp._ COWS' MILK, of average quality, contains from 10% to 12% of solid matter when evaporated to dryness by steam heat, and has the mean sp. gr.
1030; while that of the skimmed milk is about 1035; and of the cream, 10244. (Ure.) The average CREAM of cows' milk contains 45% of butter, 35% of curd, and 92% of whey. (Berzelius.) The SKIMMED MILK consists of water, 929%; curd, 2%; sugar of milk, 35%; lactic acid, lactate of potassa, and a trace of lactate of iron, 6%, chloride of potassium, phosphate of potassa, and earthy phosphates (lime), 2%. (Berzelius.)
The following analysis of fresh milk is by M. Haidlen:--
Water 87300 Butter 3000 Casein 4820 Milk sugar 4390 Phosphate of lime 231 Phosphate of magnesia 42 Phosphate of iron 07 Chloride of potassium 144 Chloride of sodium 24 Soda in combination with casein 42 -------- 1000.
Professor Wanklyn has devised and published in his excellent little manual 'Milk Analysis'[37] a process by which a very thorough chemical examination of milk may be accomplished with great facility and expedition.
[Footnote 37: Trubner and Co.]
In his preliminary remarks he condemns, as utterly unreliable and misleading, the inferences to be drawn from those hydrometric instruments, the lactometer or lactodensimeter, and creamometer. "A very little consideration," he says "will suffice to make intelligible the obliquity of the indications of the lactometer and to show how untrustworthy it must be. The lactometer, as of course will be understood, is simply the hydrometer applied to milk; and readings of the instrument are neither more nor less than specific gravities. The more milk-sugar, and casein, and mineral matter there is in a given specimen of milk, the greater (other things being equal) will be its density or specific gravity, and the higher the lactometer reading.
"If, however, fat globules (as happens in the instance of milk) be diffused through the fluid, then, because fat is lighter than water, the effect of the other milk solids on the gravity of the liquid, will be more or less neutralised. The density of milk-fat is about 09, water being 10. Now, if a solution of casein and milk-sugar, of specific gravity 1030, be sufficiently charged with fat globules, its specific gravity may be sent down even below the gravity of water. How much would be required to bring about such a result is a matter of simple calculation.
"This being understood, it will be obvious that if the specimens of milk differ in specific gravity, there must be two distinct and equally valid ways of accounting for the difference.
"The milk with the lower gravity may be milk let down with water, or let down with fat, _i. e._ milk let down by being enriched."
In support of this last assertion Professor Wanklyn quotes corroborative instances afforded by the examination of different specimens of milk known as 'strippings,' these being the last portions of milk yielded by the cow at the termination of the milking. All these 'strippings' had a lower specific gravity than normal milk.
Further, Professor Wanklyn points out that the specific gravity of organic fluids is a fallacious index of the amount of solids they may contain, as is illustrated by the fact, that whilst a 10 per cent. solution of chloride of potassium has a specific gravity of 1065 at 15 C., and a 10 per cent. solution of casein and milk sugar, has a specific gravity of only about 1035.
The creamometer meets with equal condemnation in Professor Wanklyn's little book, since different specimens of milk vary considerably in their yield of cream, and a perfectly pure sample of milk may yield less cream than one which has been tampered with.
A complete analysis of milk involves the determination of the water, the fat (the essential constituent of the cream), the casein, milk-sugar, and ash.
The following is an outline of Professor Wanklyn's neat and ingenious method of analysis:--
By means of an accurately graduated pipette, he first places 5 cubic centimetres of the milk in a small weighed platinum dish (about 14 grammes in weight) just previously ensuring the sample from which the milk is taken being thoroughly mixed.
The dish is then placed over a water-bath (the water in which must be kept vigorously boiling the whole time) for three hours, at the end of which time all the water having been driven off, there will remain in the dish a completely dried up residue.
The increase in weight between the empty dish and the residue, will give the weight of the 'milk solids' from 5 c.c. of milk. Of course, if this weight be multiplied by 20, the yield from 100 c.c. of milk will be obtained.
To reduce this to a percentage statement it is necessary to remember that 100 c.c. of average milk weigh 1029 grammes. The next proceeding consists in the determination of the fat. This is done by treating the dried milk solids resulting from the 5 c.c. of milk with ether. There are several important minutiae necessary to be observed in connection with this part of the process, for the particulars of which the reader is referred to Professor Wanklyn's book. Suffice it to say, that if properly performed, the whole of the fat is dissolved by the ether, and being separated from the non-fatty portion of the residue is weighed and calculated as 'fat.'
If, then, the amount found as fat be deducted from the whole of the milk solids previous to their treatment with ether, the 'milk solids, not fat,'
will be arrived at. Professor Wanklyn estimates the casein[38] as follows:--He treats the milk solids, not fat, with hot alcohol, by which means he dissolves out from them, and removes the milk-sugar and the soluble chlorides. The remaining residue, consisting of casein and phosphate of sodium (chemically combined with the casein), is dried on a water-bath until it ceases to lose weight. It is then weighed along with the vessel containing it, and ignited. The combined weight of the vessel and phosphate of sodium remaining after ignition being deducted from the weight previous to ignition, the difference is the casein.
[Footnote 38: Under the head "Casein" Prof Wanklyn includes the entire nitrogenous materials of milk.]
Another and quicker method, recommended by Professor Wanklyn, for the determination of the casein, is to measure it by the amount of albuminoid ammonia it is capable of yielding when subjected to the 'albuminoid ammonia process,' invented by Messrs Wanklyn, Chapman, and Smith.
The alcoholic solution filtered off from the combined casein and phosphate of sodium, contains the milk sugar and soluble chlorides. It is evaporated to dryness on a water-bath, and the residue with the vessel containing it, is weighed. It is then gently ignited, and the weight of the remaining residue being deducted from the total weight before ignition, gives the yield of milk sugar. Or the milk sugar may be determined by titration with a standard copper solution.
For the determination of the ash it is only necessary to ignite the milk solids from 5 c.c. of milk, in the small platinum dish, by which operation all the organic matter being driven off, that which remains behind constitutes the 'ash' and is weighed as such.
It will be obvious that in order to determine with anything like rigid accuracy the quality of any sample of milk by analysis, not only must a normal standard for the purpose of comparison be adopted, but such normal standard must represent very closely and with but little variation the definite composition of all sound and genuine milk.
Professor Wanklyn says that "the following, which is the result of several concordant analyses of country-fed milk, may be taken as representing normal milk. In 100 grammes of milk--
Solids (dry at 100 C) 125 grammes.
Water 875 ------ 1000
"The 125 grammes consist of 93 grammes of 'solids which are not fat,'
and 32 grammes of fat." The above data, which are founded on the examination of a very large number of different samples of milk, are confirmed by the researches of Muller and Eisenstuck, who were employed by the Royal Agricultural Society of Sweden in a similar investigation. The labours of these chemists extended over a twelvemonth, and the result of them was to show that the milk yielded day by day, for a whole year, by a herd of cows was remarkably constant in composition.
Professor Wanklyn gives the following formulae for the calculation and statement of the results of milk analysis. He says, treating the question quite rigidly, which I believe is the proper way of dealing with it, we arrive at the following:--
_Problem_ 1. Given the percentage of 'solids, not fat' (= _a_), in a specimen of sophisticated milk (_i. e._ milk, either watered, or skimmed, or both)--required the number of grammes of genuine milk which was employed to form 100 grammes of it.
_Answer._ Multiply the percentage of 'solids, not fat' by 100, and divide by 93.
Or-- (100 / 93)_a_.
_Problem_ II.--Given the percentage of 'solids, not fat' (= _a_), also the percentage of fat (= _b_), in a specimen of sophisticated milk--required the number of grammes of fat which have been removed by skimming from the genuine milk which was employed to form 100 grammes of it.