PLATE IX

FOOTNOTES:

[50] ‘Bread Analysis.’

[51] Wanklyn applies his ammonia process (see p. 205), to the estimation of albuminoids in vegetable substances. In this manner he obtained the following percentages of ammonia from various flours:--Rice, 0·62; maize and malt, 1·03; wheat and barley, 1·10; rye, 1·45; pea, 2·30.

[52] ‘An Investigation of the Composition of American Wheat and Corn.’ United States Department of Agriculture, 1883.

[53] ‘Die Menschlichen Nahrungs- und Genussmittel’ p. 420. Berlin, 1883.

BAKERS’ CHEMICALS.

The substances employed for the artificial production of porosity in bread, as already mentioned, are sodium bicarbonate (now termed “saleratus”), potassium bitartrate, tartaric acid, and calcium diphosphate, the various mixtures of these compounds being known as baking powders. Some of the above chemicals are not always used in the pure state, and, in addition to this source of contamination, baking powders are often excessively diluted with flour or starch, and seriously adulterated with alum.

The sodium bicarbonate employed is generally a fairly pure article. Common grades of the salt contain a little sodium chloride, and in some cases as much as 2 per cent. of the corresponding sulphate; it may also prove to be somewhat deficient in the proportion of carbonic acid present. Cream of tartar (potassium bitartrate), is far more liable to adulteration. A certain quantity of calcium tartrate is often found in the commercial article, originating from its method of manufacture, and amounting, on the average, from 6 to 7 per cent. The salt is, moreover, sometimes intentionally mixed with alum, starch, tartaric acid, gypsum, chalk and terra alba.

Occasionally so-called cream of tartar has been found to be wholly composed of starch and calcium diphosphate. In the examination for calcium tartrate and sulphate, a quantitative determination of the total lime and sulphuric acid is made. The quantity of sulphuric acid obtained is calculated to gypsum, any excess of lime left being returned as tartrate. The ash in pure cream of tartar should amount to 36·79 per cent., while that of calcium tartrate is only 21·54 per cent. Naturally, the addition of flour or starch would materially decrease the proportion of ash. The presence of these latter adulterants is recognised by means of the microscope, and by testing the sample with iodine solution. It is generally required that cream of tartar should contain at least 90 per cent. of potassium bitartrate.

_Baking powders._--The usual composition of baking powders has already been stated. They all contain sodium bicarbonate, but differ in the acid ingredient present, which may consist of cream of tartar, tartaric acid, calcium diphosphate, or alum. In order to remedy the tendency to deterioration which exists in powders entirely composed of the above salts, it is the practice to add a considerable amount of “filling” (corn-starch, flour, etc.). The quantity of filling employed for this purpose varies from 20 to 60 per cent., but is as a rule, greater than is really necessary. A small proportion of the sodium salt is often replaced by ammonium sesquicarbonate. Alum is a more objectionable constituent of many preparations, and it should be considered an adulteration. The practical value of baking powder is chiefly dependent upon the quantity of carbonic acid it liberates when decomposed, and this is affected by the strength of the acid salt and the amount of “filling” used. The most common varieties of baking powders are:--

(_a_) _Sodium bicarbonate and cream of tartar_, either pure or mixed with starch. In testing this class of powders, it is usual to determine the excessive alkalinity remaining after the decomposition with water, by means of decinormal acid; this is put down as bicarbonate present in excess. The proportions of sodium bicarbonate and cream of tartar are calculated from the alkaline strength of the ash, minus the excessive alkalinity found.

Impurities originating from the cream of tartar employed are estimated as previously described; and the amount of starch contained is determined by the usual methods. In some preparations, tartaric acid is substituted for cream of tartar.

The following proportions represent the composition of a baking powder of good quality:--

Parts. Cream of tartar 30 Sodium bicarbonate 15 Flour 5

(_b_) _Sodium bicarbonate and calcium diphosphate._--Calcium sulphate occurs as an impurity in the commercial phosphate and is therefore liable to be met with in phosphate powders. In addition to phosphoric acid, lime, etc., a determination of sulphuric acid and chlorine should be made.

(_c_) _Sodium bicarbonate and alum._--These constitute the most reprehensible forms of baking powder. The sanitary effects of alum have been referred to under Flour. It may be present either as potash or ammonia alum. The following is a fair example of an alum powder:--

Per cent. Alum 26·45 Sodium bicarbonate 24·17 Ammonium sesquicarbonate 2·31 Cream of tartar None Starch 47·07

From an exhaustive investigation of baking powders made by Dr. Henry A. Mott, it was found that about 50 per cent. of these preparations were impure, alum being the chief admixture. Of 280 samples of cream of tartar lately examined by various American Health Boards, 100 were adulterated; of 95 baking powders tested, 16 were adulterated.

The sugars of commerce may be conveniently classified into two varieties, viz., sucrose (cane sugar or saccharose) and dextrose (grape sugar or glucose). The former, which is the kind almost exclusively employed for domestic uses, is chiefly obtained from the sugar cane of the West Indies and American Southern States (_Saccharum officinarum_), and, in continental Europe, from the sugar beet (_Beta vulgaris_). A comparatively small quantity is manufactured in the United States from the sugar maple (_Acer saccharinum_), and from sorghum (_Sorghum saccharatus_).

_Cane Sugar_ (C_{12} H_{22} O_{11}).--Among the more important chemical properties of cane sugar are the following:--It dissolves in about one-third its weight of cold water--much more readily in hot water--and is insoluble in cold absolute alcohol. From a concentrated aqueous solution it is deposited in monoclinic prisms, which possess a specific gravity of 1·580. Cane sugar is characterised by its property of rotating the plane of a ray of polarised light to the right; the rotary power is 66°·6. Upon heating its solution with dilute mineral acids, it is converted into a mixture termed “invert sugar,” which consists of equal parts of _dextrose_ and _levulose_. The former turns the plane of polarised light to the right, the latter to the left; but owing to the stronger rotation exerted by the levulose, the combined rotary effect of invert sugar is to the left, _i. e._, opposite to that possessed by cane sugar. Invert sugar exhibits the important property of reducing solutions of the salts of copper, which is not possessed by pure cane sugar. Cane sugar melts at 160°; at a higher temperature (210°) it is converted into a reddish-brown substance termed _caramel_. When subjected to the action of ferments, cane sugar is first transformed into invert sugar, then into alcohol and carbonic acid, according to the reactions:--

(_a_) C_{12} H_{22} O_{11} + H_{2}O = 2 C_{6} H_{12} O_{6}. (_b_) C_{6} H_{12} O_{6} = 2 CO_{2} + 2 C_{2} H_{6}O.

The varieties of cane sugar usually met with in commerce are the following:--

1. Loaf sugar, consisting either of irregular fragments, or (more often) of cut cubes.

2. Granulated sugar.

3. Soft white sugar.

4. Brown sugar, varying in colour from cream-yellow to reddish-brown.

Molasses is a solution of sugar, containing invert sugar, gummy matters, caramel, etc., which forms the mother-liquor remaining after the crystallisation of raw cane sugar; the name “syrup” being commonly applied to the residual liquor obtained in the manufacture of refined sugar.

_Dextrose_ (C_{6} H_{12} O_{6}), occurs ready-formed in grape juice, and in many sweet fruits, very frequently associated with levulose; it is also contained in honey, together with a small amount of cane sugar. As already mentioned, it constitutes an ingredient of the product obtained by the action of acids and ferments upon cane sugar. For commercial purposes, glucose is prepared by treating grains rich in starch, with dilute acids. In France and Germany, potatoes are used in its manufacture; in the United States, Indian corn or maize is almost exclusively employed. The processes used consist substantially in first separating the starch from the grain by soaking, grinding, and straining, then boiling it, under pressure, with water containing about 3 per cent. of sulphuric acid, neutralising the remaining acid with chalk, decolorising the solution by means of animal charcoal, and concentrating it in vacuum pans. In the United States thirty-two factories are engaged in the manufacture of glucose, which consume about 40,000 bushels of corn daily, their annual production having an estimated value of 10 millions of dollars. In commerce, the term grape sugar is applied to the solid product, the syrup or liquid form being known as glucose. The chief uses of starch sugar and glucose are in the manufacture of table syrups, and as a substitute for malt in the brewing of beer and ale. Their other most important applications are as a substitute for cane sugar in confectionery, and in the preparation of fruit jellies; as an adulterant of cane sugar, as an admixture to genuine honey, and as a source for the preparation of vinegar.

Dextrose is soluble in 1-1/5 part of cold water, and is much more soluble in hot water. It has a dextro-rotary power of 56°. When separated from its aqueous solution, it forms white and opaque granular masses, but from an alcoholic solution, it is obtained in well-defined, microscopic needles, which fuse at 146°. Two parts of glucose have about the same sweetening effect as one part of cane sugar.[54] It does not become coloured when mixed with cold concentrated sulphuric acid, which distinguishes it from sucrose; on the other hand, its solution is coloured dark-brown if boiled with potassium hydroxide, another distinction from cane sugar. Dextrose is capable of directly undergoing vinous fermentation, and, like invert sugar, it possesses the property of reducing alkaline solutions of copper salts, especially upon the application of heat.

The chief commercial varieties of American glucose are the following:--

1. _Glucose_: Per cent. Glucose. “Crystal H,” containing 40 “Crystal B” 45 “Crystal A” 50

2. _Grape Sugar_: “Brewers’ grape” 70-75 “A” or “Solid grape” 75-80 “Grained” or “Granulated grape” 80-85

_Maltose_ and _levulose_ are isomers of dextrose. The former is prepared by the action of malt or diastase upon starch. It has a dextro-rotary power of 150° and its property of reducing copper salts is only about 60 per cent. of that of dextrose. It is converted into the latter compound upon boiling with dilute sulphuric acid. Levulose, as previously stated, is formed, together with dextrose, from cane sugar by treatment with dilute acids or with ferments. It turns the plane of a ray of polarised light to the left, its rotary power varying considerably at different temperatures.

_Lactose_, or milk sugar, has already been referred to under the head of Milk. It is isomeric with cane sugar, possesses a dextro-rotary power (58°·2), and undergoes fermentation when mixed with yeast, and reduces alkaline copper solutions, but in a different degree from glucose.

Many of the substances frequently enumerated as being used to adulterate sugar are at present very seldom employed. The usual list includes “glucose” (often meaning invert sugar), sand, flour, chalk, terra alba, etc. Loaf sugar is almost invariably pure, although its colour is sometimes improved by the addition of small proportions of various blue pigments, such as ultramarine, indigo, and Prussian blue. The presence of ultramarine was detected in about 73 per cent. of the samples of granulated sugar tested in 1881 by the New York State Board of Health. Tin salts[55] are also occasionally employed in the bleaching of sugar and syrups. Granulated sugar is asserted to be sometimes mixed with grape sugar, and powdered sugar has been found adulterated with flour and terra alba; but the varieties which are most exposed to admixture are the low grades of yellow and brown sugar, in which, however, several per cent. of invert sugar are normally present. Sand, gravel, and mites form a rather common contamination of raw sugar. From the year 1876 to 1881, 310 samples of commercial sugar were examined by the public health authorities of Canada, of which number 24 were reported as containing glucose, and 11 as of doubtful purity. Of 38 samples of brown sugar recently analysed by Dr. Charles Smart, of the National Board of Health, 9 were adulterated with glucose. From the investigations of A. L. Colby, Analyst to the New York State Board of Health, it was found that of the 116 samples examined, the white sugars were practically pure; whereas, of 67 samples of brown sugar, 4 contained glucose. Of 16 specimens of brown sugar, tested by a commission appointed by the National Academy of Sciences in 1883, 4 contained about 30 per cent. of this body.[56] Many varieties of sugar-house syrups, and the various forms of confectionery, are very extensively adulterated with artificial glucose.

The average sugar-house syrup has the following composition:--

Per cent. Water 16 Crystallisable sugar 36 Invert sugar 34 Gum, pectose, etc. 10 Ash 4

Dr. W. H. Pitt, in the Second Annual Report of the New York State Board of Health, gives the following analysis of grocers’ mixed glucose syrup, and of confectioners’ glucose:--

_American Grape Sugar Co.’s Syrup._

Per cent. Ash 0·820 Water 18·857 Dextrine 34·667 Cane syrup 7·805 Glucose 37·851 ------- 100·000 -------

_Confectioners’ Glucose._

Per cent. Ash 0·431 Water 15·762 Dextrine 41·614 Glucose 42·193 ------- 100·000 -------

It is stated that a large proportion of the American maple syrup and maple sugar found on the market, consists of raw sugar, flavoured with the essential oil of hickory-bark, for the manufacture of which letters patent have been granted.

_Analysis of Sugar._--The examination of sugar is ordinarily confined to the estimation of the water, ash, and determination of the nature of the organic matters present. The proportion of water contained in a sample is found by drying it for about two hours in an air-bath, at a temperature of 110°. Moist and syrupy sugars, such as muscovadoes, are advantageously mixed with a known weight of ignited sand before drying. The ash is determined either by directly incinerating a few grammes of the sugar in a tared platinum capsule, or by accelerating the process of combustion by first moistening the sample with a little sulphuric acid. In this case the bases will naturally be converted into sulphates, and a deduction of one-tenth is usually made from the results so obtained, in order to reduce it to terms of the corresponding carbonates. The proportion of ash in raw cane sugar varies somewhat, but it should not much exceed 1·5 per cent. Its average composition, as given by Monier, is as follows:--

Calcic carbonate 49·00 Potassium carbonate 16·50 Sodium and potassium sulphates 16·00 Sodium chloride 9·00 Alumina and silica 9·50 ------ 100·00 ------

Insoluble mineral adulterants are readily separated by dissolving a rather considerable amount of the sample in water and filtering. In this manner the presence of sand, terra alba, and foreign pigments may be recognised.

The determination of the character of the organic constituents of commercial sugars is effected, either by chemical or by physical tests, and, in some instances, by a combination of these methods. The presence of such adulterants, as flour or starch, is very easily detected upon a microscopic examination of the suspected sample.

If cane sugar, containing grape sugar, is boiled with water, to which about 2 per cent. of potassium hydroxide has been added, the solution acquires a brown colour.

Upon mixing a solution of pure cane sugar with a solution of cupric sulphate, adding an excess of potassium hydroxide, and boiling, only a slight precipitation of red cupric oxide takes place. Under the same conditions, grape sugar at once produces a copious green precipitate, which ultimately changes to red, the supernatant fluid becoming nearly or quite colourless. A very good method for the quantitative estimation of grape sugar when mechanically mixed with cane sugar, is that of P. Casamajor. It is executed by first preparing a saturated solution of grape sugar in methylic alcohol. The sample to be tested is thoroughly dried, and then well agitated with the methylic alcohol solution, in which all cane sugar will dissolve; any grape sugar present remains behind, and upon allowing the mixture to remain at rest for a short time, forms a deposit which is again treated with the grape sugar solution, and then collected upon a tared filter, washed with absolute methylic alcohol, and weighed. Glucose and invert sugar are usually quantitatively determined by means of Fehling’s solution.

As this preparation is liable to decompose upon keeping, it is advisable to first prepare cupric sulphate solution by dissolving exactly 34,640 grammes of the salt in 500 c.c. of distilled water, and then make up the Rochelle salt solution by dissolving 68 grammes of sodium hydroxide, and 173 grammes of Rochelle salt in 500 c.c. of water, the solutions being kept separate. When required for use, 5 c.c. each of the copper and Rochelle solutions (corresponding to 10 c.c. of Fehling’s solution) are introduced into a narrow beaker, or a porcelain evaporating dish, a little water is added, and the liquid brought to the boiling point. The sugar solution under examination should not contain over 0·5 per cent. of glucose. It is cautiously added to the hot Fehling’s solution from a burette until the fluid loses its blue colour (see p. 37). The number of c.c. required to completely reduce 10 c.c. of Fehling’s solution, represents 0·05 gramme of grape sugar. The foregoing volumetric method is sometimes applied gravimetrically by adding a slight excess of Fehling’s solution to the sugar solution, collecting the precipitated cupric oxide upon a filter and weighing, after oxidation with a few drops of nitric acid; or, it may be dissolved, and the copper contained deposited by electrolysis, in which case the weight of copper obtained, multiplied by 0·538, gives the equivalent amount of glucose. The proportion of cane sugar in a sample of raw sugar can be determined by first directly estimating the proportion of invert sugar contained by means of Fehling’s solution, as just described. The cane sugar present is then inverted by dissolving one gramme of the sample in about 100 c.c. of water, adding 1 c.c. of strong sulphuric acid, and heating the solution in the water-bath for 30 minutes, the water lost by evaporation being from time to time replaced. The free acid is next neutralised by a little sodium carbonate, its volume made up to 200 c.c., and the invert sugar now contained est

Commercial cane sugar is, however, generally estimated by the instrument known as the saccharimeter or polariscope.

In order to convey an intelligent idea of the physical laws which govern the practical working of the polariscope, it will first be necessary to refer to the subject of the polarisation of light. The transformation of ordinary into polarised light is best effected either by reflection from a glass plate at an angle of about 56°, or by what is known as double refraction. The former method can be illustrated by Fig. 1, Plate X., which represents two tubes, B and C, arranged so as to allow the one to be turned round within the other. Two flat plates of glass, A and P, blackened at the backs, are attached obliquely to the end of each tube at an angle of about 56°, as represented in the figure. The tube B, with its attached plate, A, can be turned round in the tube C without changing the inclination of the plate to a ray passing along the axis of the tube. If a candle be now placed at I, the light will be reflected from the plate P through the tube, and, owing to the particular angle of this plate, will undergo a certain transformation in its nature, or, in other words, become “polarised.” So long as the plate A retains the position represented in the figure, the reflected ray would fall in the same plane as that in which the polarisation of the ray took place, and an image of the candle would be seen by an observer stationed at O. But, suppose the tube B to be turned a quarter round; the plane of reflection is now at right angles to that of polarisation, and the image will become invisible. When the tube B is turned half-way round, the candle is seen as brightly at first; at the third quadrant it disappears, until, on completing the revolution of the tube, it again becomes perfectly visible. It is evident that the ray reflected from the glass plate P has acquired properties different from those possessed by ordinary light, which would have been reflected by the plate A in whatever direction it might have been turned.