Chapter 8

The ethers proper would also be placed in a new light by this new conception of the constitution of the water molecule. The hydrogen in the hydroxyl group, as is known, may be substituted by an alkyl group. For instance, an alkyl may be substituted for the hydroxyl hydrogen in an alcohol molecule, when an ether results. According to the new theory this ether will no longer be considered as two alkyl groups connected by an oxygen atom, but as a compound built up on the type of water by the union of an alkyl group and an alkoxyl group. Thus ethylic ether would not be represented by

C_{2}H_{5} > O, C_{2}H_{5}

as heretofore, but by the formula C_{2}H_{5}(OC_{2}H_{5}), which is ethyl-ethoxol. Acetone would admit of a similar explanation.

Finally the assumption of dissimilarity in character of the hydrogen atoms in the water molecule possibly may lead to the discovery of a number of unlocked for isomerides.

Thus, by appropriate methods, it ought to become possible to introduce the alkyl groups solely into the hydroxyl group (instead of into the place of the loosely attached H-atom). In that case chemists might arrive at an isomeride of methyl alcohol of the formula H.(OCH_{3}), or at methoxyl hydride, a compound not alcoholic in character, or at a nitroxyl hydride, H(ONO_{2}), not of an acidic nature. Oxychlorides would be classed with this latter category, that is, they would be looked on as water in which the free hydrogen atom has been substituted by the metal, and the hydrogen atom of the hydroxyl by chlorine. This example, indeed, furnishes a most characteristic illustration of our theory. In the case just now assumed we arrive at the oxychloride; when, however, the metal and chlorine change places in the water molecule, the isomeric hypochlorous salts are the result. It is true that such cases of isomerism are as yet unknown, but we do know that certain metals, in our present state of knowledge, yield oxychlorides only, while others only form hypochlorous salts. This condition also explains why hypochlorites still possesses the bleaching power of chlorine, while the same is not true of oxychlorides. However, it seems needless to multiply examples in further illustration of the theory.

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THE FORMATION OF STARCH IN LEAVES.

In 1750, Bonnet, a Genevese naturalist, remarked that leaves immersed in water became covered in the sun with small bubbles of a gas that he compared to small pearls. In 1772, Priestley, after discovering that the sojourn of animals in a confined atmosphere renders it irrespirable, investigated the influence of plants placed in the same conditions, and he relates, in these words, the discovery that he made on the subject:

"I put a sprig of mint in a quantity of air in which a candle had ceased to burn, and I found that, ten days later, another candle was able to burn therein perfectly well." It is to him, therefore, that is due the honor of having ascertained that plants exert an action upon the atmosphere contrary to that exerted by animals. Priestley, however, was not completely master of his fine experiment; he was ignorant of the fact, notably, that the oxygen is disengaged by plants only as long as they are under the influence of light.

This important discovery is due to Ingenhouse. Finally, it was Sennebier who showed that oxygen is obtained from leaves only when carbonic acid has been introduced into the atmosphere where they remain. Later on, T. De Saussure and Boussingault inquired into the conditions most favorable to assimilation. Boussingault demonstrated, in addition, that the volume of carbonic acid absorbed was equal to that of the oxygen emitted. Now we know, through a common chemical experiment, that carbonic acid contains its own volume of oxygen. It was supposed, then, that carbonic acid was decomposed by sunlight into carbon and oxygen. Things, however, do not proceed so simply. In fact, it is certain that, before the complete decomposition into carbon and oxygen, there comes a moment in which there is oxygen on the one hand and oxide of carbon (CO_{2} = O + CO) on the other.

The decomposition, having reached this point, can go no further, for the oxide of carbon is indecomposable by leaves, as the following experiment proves.

If we put phosphorus and some leaves into an inert gas, such as hydrogen, we in the first place observe the formation of the white fumes of phosphoric acid due to the oxidation of the phosphorus by the oxygen contained in the leaves. This phosphoric acid dissolves in the water of the test glass and the latter becomes transparent again. If, now, we introduce some oxide of carbon, we remark in the sun no formation of phosphoric acid, and this proves that there is no emission of oxygen.

This latter hypothesis of the decomposition of carbonic acid into a half volume of vapor of carbon and one volume of oxygen being rejected, the idea occurred to consider the carbonic acid in a hydrated state and to write it CO_{2}HO.

In this case, we should have by the action of chlorophyl: 2CO_{2}HO (carbonic acid) = 4O (oxygen) + C_{2}H_{2}O_{2} (methylic aldehyde).

This aldehyde is a body that can be polymerized, that is to say, is capable of combining with itself a certain number of times to form complexer bodies, especially glucose. This formation of a sugar by means of methylic aldehyde is not a simple hypothesis, since, on the one hand, Mr. Loew has executed it by starting from methylic aldehyde, and, on the other, we find this glucose in leaves by using Fehling's solution.

The glucose formed, it is admissible that a new polymerization with elimination of water produces starch. The latter, in fact, through the action of an acid, is capable of regenerating glucose.

It may, therefore, be supposed that the decomposition of carbonic acid by leaves brings about the formation of starch through the following transformations: (1) The decomposition of the carbonic acid with emission of oxygen and production of methylic aldehyde; (2) polymerization of methylic aldehyde and formation of glucose; (3) combination of several molecules of glucose with elimination of water; formation of starch.

Starch is thus the first stable product of chlorophylian activity. Is there, in fact, starch in leaves? It is easy to reveal its presence by the blue coloration that it assumes in contact with iodine in a leaf bleached by boiling alcohol.

Mr. Deherain has devised a nice method of demonstrating that this formation of starch, and consequently the decomposition of carbonic acid, can occur only under the influence of sunlight. He pointed it out to us in his course of lectures at the School of Grignon, and asked us to repeat the experiment. We succeeded, and now make the _modus operandi_ known to our readers.

The leaf that gave the best result was that of the _Aristolochia Sipho_. The leaf, adherent to the plant, is entirely inclosed between two pieces of perfectly opaque black paper. That which corresponds to the upper surface of the limb bears cut-out characters, which are here the initials of Mr. Deherain. The two screens are fastened to the leaf by means of a mucilage of gum arabic that will easily cede to the action of warm water at the end of the experiment.

The exposure is made in the morning, before sunrise. At this moment, the leaf contains no starch; that which was formed during the preceding day has emigrated during the night toward the interior of the plant.

After a few hours of a good insolation, the leaf is picked off. Then the gum which holds the papers together is dissolved by immersion in warm water. The decolorizing is easily effected through boiling alcohol, which dissolves the chlorophyl and leaves the leaf slightly yellowish and perfectly translucent.

There is nothing more to do then but dip the leaf in tincture of iodine. If the insolation has been good, and if the screens have been well gummed so that no penumbra has been produced upon the edge of the letters, a perfectly sharp image will be instantly obtained. The excess of iodine is removed by washing with alcohol and water, and the leaf is then dried and preserved between the leaves of a book.

It is well before decolorizing the leaf to immerse it in a solution of potassa; the chlorophylian starch then swells and success is rendered easier.--_Lartigue and Malpeaux, in La Nature_.

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STANDARDS AND METHODS FOR THE POLARIMETRIC ESTIMATION OF SUGARS.[1]

[Footnote 1: Report to the United States Internal Revenue Department by C.A. Crampton, Chemist of U.S. Internal Revenue; H.W. Wiley, Chief Chemist of U.S. Department of Agriculture; and O.H. Tittmann, Assistant in Charge of Weights and Measures, U.S. Coast and Geodetic Survey.]

Section 1, paragraph 231, of the act entitled "An act to reduce revenue and equalize duties on imports and for other purposes," approved October 1, 1890, provides:

"231. That on and after July 1, eighteen hundred and ninety-one, and until July 1, nineteen hundred and five, there shall be paid, from any moneys in the Treasury not otherwise appropriated, under the provisions of section three thousand six hundred and eighty-nine of the Revised Statutes, to the producer of sugar testing not less than ninety degrees by the polariscope, from beets, sorghum, or sugar cane grown within the United States, or from maple sap produced within the United States, a bounty of two cents per pound; and upon such sugar testing less than ninety degrees by the polariscope, and not less than eighty degrees, a bounty of one and three-fourth cents per pound, under such rules and regulations as the Commissioner of Internal Revenue, with the approval of the Secretary of the Treasury, shall prescribe."

It is the opinion of this Commission that the expression "testing ... degrees by the polariscope," used with reference to sugar in the act, is to be considered as meaning the percentage of pure sucrose the sugar contains, as ascertained by polarimetric estimation.

It is evident that a high degree of accuracy is necessary in the examination of sugars by the Bureau of Internal Revenue, under the provisions of this act, inasmuch as the difference of one-tenth of one per cent. in the amount of sucrose contained in a sugar may, if it is on the border line of 80°, decide whether the producer is entitled to a bounty of 1¾ cents per pound (an amount nearly equivalent to the market value of such sugar) or to no bounty whatever. It is desirable, therefore, that the highest possible degree of accuracy should be secured in the work, for while many sugars will doubtless vary far enough from either of the two standard percentages fixed upon in the act, viz., 80° and 90°, to admit of a wide margin of error without material consequences, yet a considerable proportion will approximate to them so closely that a difference of a few tenths of a degree in the polarization will change the classification of the sugar.

A very high degree of accuracy may be obtained in the optical estimation of sugars, if the proper conditions are observed. Such conditions are (1) accurately graded and adjusted instruments, weights, flasks, tubes, etc.; (2) skilled and practiced observers; (3) a proper arrangement of the laboratories in which the work is performed; and (4) a close adherence to the most approved methods of manipulation.

On the other hand, if due observance is not paid to these conditions, the sources of error are numerous, and inaccurate results inevitable.

We will endeavor to point out in this report the best means of meeting the proper conditions for obtaining the highest degree of accuracy consistent with fairly rapid work. It would be manifestly impossible to observe so great a refinement of accuracy in this work as would be employed in exact scientific research.

This would be unnecessary for the end in view, and impossible on account of the amount of time that would be required.

I.--INSTRUMENTS AND APPARATUS.

It is of the greatest importance that the polariscopes and all apparatus used in the work shall be carefully and accurately adjusted and graduated, and upon a single and uniform system of standardization. Recent investigations of the polarimetric work done in the customs branch of the Treasury Department have shown that a very considerable part of the want of agreement in the results obtained at the different ports was due to a lack of uniformity in the standardization of the instruments and apparatus.

_(a.) The Polariscope._--There are many different forms of this instrument used. Some are adapted for use with ordinary white light, and some with monochromatic light, such as sodium ray. They are graduated and adjusted upon various standards, all more or less arbitrary. Some, for example, have their scales based upon the displacement of the polarized ray produced by a quartz plate of a certain thickness; others upon the displacement produced by an arbitrary quantity of pure sucrose, dissolved and made up to a certain volume and polarized in a certain definite length of column. It would be very desirable to have an absolute standard set for polariscopic measurements, to which all instruments could be referred, and in the terms of which all such work could be stated. This commission has information that an investigation is now in progress under the direction of the German imperial government, having for its end and purpose the determination of such data as will serve for the establishment of an absolute standard. When this is accomplished it can easily be made a matter of international agreement, and all future forms of instruments be based upon it. This commission would suggest that the attention of the proper authorities should be called to the desirability of official action by this government with a view to co-operation with other countries for the adoption of international standards for polarimetric work. Until this is done, however, it will be necessary for the Internal Revenue Bureau to adopt, provisionally, one of the best existing forms of polariscope, and by carefully defining the scale of this instrument, establish a basis for its polarimetric work which will be a close approximation to an absolute standard, and upon which it can rely in case of any dispute arising as to the results obtained by the officers of the bureau.

For the instrument to be provisionally adopted by the Internal Revenue Bureau, this commission would recommend the "half shadow" instrument made by Franz Schmidt & Haensch, Berlin. This instrument is adapted for use with white light illumination, from coal oil or gas lamps. It is convenient and easy to read, requiring no delicate discrimination of colors by the observer, and can be used even by a person who is color blind.

This form of instrument is adjusted to the Ventzke scale, which, for the purposes of this report, is defined to be such that 1° of the scale is the one hundredth part of the rotation produced in the plane of polarization of white light in a column 200 mm. long by a standard solution of chemically pure sucrose at 17.5° C. The standard solution of sucrose in distilled water being such as to contain, at 17.5° C. in 100 c.c., 26.048 grms. of sucrose.

In this definition the weights and volumes are to be considered as absolute, all weighings being referred to a vacuum.

The definition should properly be supplemented with a statement of the equivalent circular rotation in degrees, minutes, and seconds that would be produced by the standard solution of sugar used to read 100° on the scale. This constant is now a matter of investigation, and it is thought best not to give any of the hitherto accepted values. When this is established, it is recommended that it be incorporated in a revision of the regulations of the internal revenue relative to sugar, in order to make still more definite and exact the official definition of the Ventzke scale.

The instruments should be adjusted by means of control quartz plates, three different plates being used for complete adjustment, one reading approximately 100° on the scale, one 90°, and one 80°.

These control quartz plates should have their exact values ascertained in terms of the Ventzke scale by the office of weights and measures by comparison with the standard quartz plates in possession of that office, in strict accordance with the foregoing definition, and should also be accompanied by tables giving their values for temperatures from 10° to 35°.

_(b.) Weights._--The weights used should be of solid brass, and should be standardized by the office of weights and measures.

_(c.) Flask._--The flasks used should be of such a capacity as to contain at 17.5° C. 100.06 cubic centimeters, when filled in such a manner that the lowest point of the meniscus of the surface of the liquid just touches the graduation mark. The flasks will be standardized to contain this volume in order that the results shall conform to the scale recommended for adoption without numerical reduction of the weighings to vacuo. They should be calibrated by the office of weights and measures.

_(d.) Tubes._--The tubes used should be of brass or glass, 200 and 100 millimeters in length, and should be measured by the office of weights and measures.

_(e.) Balances._--The balances used should be sensitive to at least one milligramme.

II.--SKILLED OBSERVERS.

The commission recommends that the work of polarizing sugars be placed in the hands of chemists, or at least of persons who are familiar with the use of the polariscope and have some knowledge of the theory of its construction and of chemical manipulations. To this end we would suggest that applicants for positions where such work is to be done should be obliged to undergo a competitive examination in order to test their fitness for the work that is to be required of them.

III.--ARRANGEMENT OF LABORATORIES.

The arrangement of the rooms in which polarizations are performed has an important bearing upon the accuracy of the results obtained.

Polariscopic observations are made more readily and accurately if the eye of the observer is screened from diffused light; therefore, a partial darkening of the room, which may be accomplished by means of curtains or hangings, is an advantage. On the other hand, the temperature at which the observation is made has a very considerable influence upon the results obtained, so that the arrangements for darkening the room must not be such as will interfere with its proper ventilation. Otherwise the heat from the lamps used, if confined within a small room, will cause considerable variations in the temperature of the room from time to time.

The proper conditions will best be met, in our opinion, by placing the lamps either in a separate room from that in which the instruments are, and perforating the wall or partition between the two rooms for the light to reach the end of the instruments, or in a ventilated hood with the walls perforated in a like manner. By lining the wall or partition on both sides with asbestos paper, and inserting a plate of plane glass in the aperture through which the light passes, the increase of temperature from the radiation of the lamp will be still further avoided. With the lamps separated from the instruments in this manner, the space in which the instruments are contained is readily darkened without much danger of its temperature being unduly raised.

Some light, of course, is necessary for reading the scales, and if artificial light is employed for this purpose, the sources chosen should be such that as little heat as possible will be generated by them. Small incandescent electric lights are best for such purpose. Refinements of this kind cannot always be used, of course, but the prime requisite with reference to the avoidance of temperature errors is that all operations--filling the flasks and tubes, reading the solutions, controlling the instrument with standard quartz plates, etc.--should be done at one and the same temperature, and that this temperature be a constant one, that is, not varying greatly at different hours of the day. For example, the room should not be allowed to become cold at night, so that it is at low temperature in the morning when work is begun, and then rapidly heated up during the day. The polariscope should not be exposed to the direct rays of the sun during part of the day, and should not be near artificial sources of heat, such as steam boilers, furnaces, flues, etc.

The tables upon which the instruments stand should be level.

IV.--METHODS OF MANIPULATION.

The methods of manipulation used in the polarization of sugar are of prime importance. They consist in weighing out the sugar, dissolving it, clarifying the solution, making it up to standard volume, filtering, filling the observation tube, regulating the illumination, and making the polariscopic reading.

The proper conduct of these processes, in connection with the use of accurately graduated apparatus, is the only surety against the numerous sources of error which may be encountered. Different sugars require different treatment in clarification, and much must necessarily be left to the judgment and experience of the operator.

The following directions are based upon various official procedures such as the one used in the United States custom houses, the method prescribed by the German government, etc. They embody also the result of recent research in regard to sources of error in polarimetric estimation of sugar:

DIRECTIONS FOR THE POLARIZATION OF SUGAR.

1.--_Description of Instrument and Manner of Using._

The instrument employed is known as the half shadow apparatus of Schmidt and Haensch. It is shown in the following cut.

The tube N contains the illuminating system of lenses and is placed next to the lamp; the polarizing prism is at O, and the analyzing prism at H. The quartz wedge compensating system is contained in the portions of the tube marked F, E, G, and is controlled by the milled head M. The tube J carries a small telescope, through which the field of the instrument is viewed, and just above is the reading tube K, which is provided with a mirror and magnifying lens for reading the scale.

The tube containing the sugar solution is shown in position in the trough between the two ends of the instrument. In using the instrument the lamp is placed at a distance of at least 200 mm. from the end; the observer seats himself at the opposite end in such a manner as to bring his eye in line with the tube J. The telescope is moved in or out until the proper focus is secured, so as to give a clearly defined image, when the field of the instrument will appear as a round, luminous disk, divided into two halves by a vertical line passing through the center, and darker on one half of the disk than on the other. If the observer, still looking through the telescope, will now grasp the milled head M and rotate it, first one way and then the other, he will find that the appearance of the field changes, and at a certain point the dark half becomes light, and the light half dark. By rotating the milled head delicately backward and forward over this point he will be able to find the exact position of the quartz wedge operated by it, in which the field is neutral, or of the same intensity of light on both halves.