REESE LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Received __ ** '' " 247 APPENDIX 249 I L L U S T E A T I ON S. XO. OF ILLUSTRATION. PAGB TRANSVERSE SECTION or RAT OF LIGHT . . . . . . . . . . 1 LINEAR POLARIZED RAY ' 1 POLARIZATION BY REFLECTION 2 RHOMBOHEDRON OF ICELAND SPAR . . . . . . . . . . 3 REFRACTION OF LIGHT BY ICELAND SPAR . . . . . . . . . . 3 710. CONSTRUCTION OF NICOL'S PRISM . . 4 11, 12. POLARIZER AND ANALYZER .. .. .. .. .. .. .. 5 13. INSTRUMENT WITH POLARIZER AND ANALYZER .. .. .. .. 6 14. PLANE OF POLARIZATION OF FIXED POLARIZER 7 10A. CONSTRUCTION OF NICOL'S PRISM . . . . . . . . . . . . 9 15. GRAPHIC REPRESENTATION OF SPECIFIC ROTATIONS . . . . . . 68 16. GRAPHIC REPRESENTATION .. .. .. .. .. .. .. 71 17. GRAPHIC REPRESENTATION .. .. .. .. .. .. .. 76 18. GBAPHIC REPRESENTATION .. .. .. ,. .. .. .. 80 1 9. GRAPHIC REPESRENTATION . . 86 20. APPARATUS FOR QUALITATIVE EXAMINATION OF ROTATORY POWER . . 96 21. MITSCHERLICH'S INSTRUMENT .. .. .. .. .. .. 99 22. LAMP FOR INSTRUMENT .... .. .. .. .. .. 99 23. VERTICAL BAND OF LIGHT .. .. .. .. .. .. .. 100 24. CHANGE OF DIRECTION OF PLANE OF POLARIZATION .. .. .. 101 25. LAMP FOR INSTRUMENT .. .. . .- .. .. .. .. 102 26. MITSCHERLICH'S LARGER INSTRUMEN .. .. .. .. .. 104 27, 28. WILD'S POLARISCOPE . . . . 107 29. ARRANGEMENT OF APPARATUS FOR OBSERVATION.. .. .. .. 109 30. PARALLEL FRINGES IN FIELD OF VISION 110 31734. RELATIVE DIRECTIONS OF ROTATION .. .. . .. .. 113 35, 3fi. RELATIVE DIRECTIONS OF ROTATION .. .. .. .. 114 XVI ILLUSTRATIONS. N'O. OF ILLUSTRATION. I'AGE 37, 38. LAURENT'S HALF-SHADE INSTRUMENT .. 118 3942. QUARTZ PLATE OF LAURENT'S INSTRUMENT 120 47, 51, 43. 44. 45. 46. 48. 49. 50. 52. 53. 54. 55. ARRANGEMENT 'OF APPARATUS FOR OBSERVATION 126 . . 129 TUBE WITH LEAD SPIRAL 130 131 MEASUREMENT OF TUBE LENGTHS BY CATHETOMETER .. 132 134 PYCNOMETER AND INDIA RUBBER BALL 139 139 MODIFIED FORM OF PYCNOMETER .. .. .. .. ,,.. 141 144 SOLEIL- VENTZKE-SCHEIBLER SACCHARIMETER . . 155 56. SOLEIL'S SACCHARIMETER WITH SCHEIBLER'S IMPROVEMENTS . . 1,39 I. INTRODUCTION. 1. In an ordinary ray of light the vibrations of the particles of ether take place successively in all possible directions perpendicular to its axis. Fig. 1 shows a transverse section of a ray, projected on a vertical plane. By certain means it is possible to restrict the vibrations to some one particular direction (Fig. 2). The ray Fig. 2. is then called a linear polarized ray. Its behaviour is no longer identically the same all around its axis, as in an ordinary ray ; on the contrary, it displays two distinct sides, one in the plane of its vibrations, the other in a plane at right angles thereto. 2. This conversion of common into polarized light may be effected, first, by reflection, for which purpose a glass mirror, inclined to the perpendicular at a certain angle (35 25'), as L M (Figs. 3 and 4), will be found best. Rays falling in the direction a b, so as to make an angle of 55 with the normal x y, are reflected in the direction b c, and at the same time are polarized. This becomes manifest when the reflected rays meet the mirror P Q, which has a rotatory movement about be as an axis. When the second mirror is parallel to the first, as in Fig. 3, the ray b c is wholly reflected in the direction c d; but as the mirror turns on its axis, the intensity of the light reflected from it diminishes, until at 90 from the starting-point there is no longer any reflection, and the mirror appears dark. Continuing the rotation, we find that at 180, B V INTRODUCTION. i.e., when the mirrors are inclined, so that the planes a b c and bed are again coincident, as in Fig. 4, there is another maximum of reflection, and, lastly, at 270 another minimum. Thus the ray Fig. 3. Q \, behaves differently in two different directions at right angles to each other, one direction being in the plane of incidence or reflection, a b c t the other in a plane at right angles therewith. The ray is polarized, and the former of the two planes is its plane of polarization. We can therefore recognize a ray as polarized, and determine the position of its plane of polarization, by permitting it to fall upon a glass mirror at an angle of 55. If the mirror be turned about the ray as an axis, light and darkness will alternate at intervals of 90, and if the mirror be set so that the light emitted by it is at its brightest, the plane passing through it and the incident polarized ray is the plane of polarization of the latter. Again, if the mirror is at its darkest, the plane at right angles to the plane of incidence of the polarized ray is coincident with the plane of polarization. By the undulatory theory of light it can be proved that the plane of polarization is either the plane in which the vibrations of ether take place, or a plane at right angles thereto. "Which of these is really the case is still an open question among physicists ; but for simplicity's sake we shall adopt the former view, and in these pages assume that the planes of vibration and polarization are coincident. 3. But a pencil of light can also be polarized by repeated INTRODUCTION. Fig. 5. single refractions or by double refraction in certain crystals, as of calc-spar the latter being the most suitable means. In a natural rhombohedron of Iceland spar (Fig. 5), the princi- pal axis lies in the line joining the points d and/, where three obtuse angles meet. Suppose a plane to pass through the shorter diagonals of two opposite faces of the rhomb, i.e., either d g, af, or d b, hf y ov d e } cf, it will invariably contain the principal axis df. Any such plane, and all planes parallel thereto, are called - Fig. G. principal sections of the prism. If a pencil of light, m n (Fig. 6), falls on one face, as a b c d (of which d b h f represents the principal section), it will, on entering the crystal, divide into two refracted rays unequally bent. Both are polarized, and application of the mirror will show that the plane of polarization (or plane of vibration) of the less refracted or extra- ordinary ray n q is perpendicular to the principal section d b hf, while that of the more highly refracted or ordinary ray n p coincides with the plane of the said section. / For polariscopic purposes it is best to give exit to one only of the two polarized rays ; that, namely, in the direction of the incident light, and to eliminate the other ray. This can be done in various ways, but most completely by converting the calc-spar into a NicoPs prism. 1 For this purpose a piece of Iceland spar is split up into an elon- gated rhombohedron, as in Fig. 7, in which the plane passing through the points abed represents a principal section. The natural ends of the prism afbe and d g c h, the former of which is inclined to a d and the latter to c b at an angle of 71, are ground so as to reduce these angles to 68 (see Fig. 8). The prism is then divided in the direction b' d, which is perpendicular to a b' and cd', and the halves 2 after polishing the faces of the section are united as before with 1 For other forms of calc-spar polarizing prisms (Senarmont's, Foucaiilt's, and "achromatized" prism) see "Wiillner's Lehrbuch der Physik, 3 Aufl. 2, 528 530. 2 Smaller Nicols may be prepared by grinding two separate crystals. B 2 Ju 4 INTRODUCTION. Canada balsam. Finally, the sides are blackened and the Nicol (Fig. 9) is fixed with cork into a brass case. ( The principal section of this prism passes through the shorter diagonals of the two rhombic ends. If a pencil of light, I m (Fig. 10), parallel to the edges of the longer side, falls on the face a b\ it divides into two rays, which are polarized at right angles to one another. The less refracted (or extraordinary) ray, m p q, traverses the film of balsam at p, and emerges in the direction q s, parallel to / m. The more refracted (or ordinary) ray. m o, meets the balsam at 0, which, from Fig. 7. Fig. 8. Fig. 9. its being a medium of so much feebler refractive power, causes total reflection of the ray in the direction o r, whereby it becomes absorbed by the case of the prism. The other ray emerges in the direction of the incident pencil, but possesses only half of its luminous power. The plane of polarization (and vibration) of this ray is at right angles to the principal section, and therefore passes through the longer diagonals of the end faces of the prism. 4. We have next to consider the behaviour of a polarized ray from a fixed Nicol, in passing through a second Nicol having a move- ment of rotation about its longitudinal axis. The first prism we will call the polarizer, the second the analyzer. INTRODUCTION. Figs. 11 and 12 show the two prisms in their cases, the principal sections being indicated by b b m, U b' n, and the planes of polarization at right angles thereto, by a a m, a a n. If we turn the analyzer A so that its plane of polarization a a' n is parallel with the plane of polarization a am of the polarizer P (Fig. 11), whereby, too, the principal sections bbm and b' b' n of the two prisms are brought into the same direction, the ray m, which enters P as ordinary light and emerges polarized at n, is not de- composed on passing through A. It is merely slightly refracted in Fig. 11. Fig. 12. the direction of an extraordinary ray m p q (Fig. 10), and emerges so at the opposite end of the analyzer. The same happens if the latter be turned through an angle of 180, so as to bring the planes again parallel. But, if the analyzer is adjusted so that its plane of polarization is at right angles to that of the polarizer that is, when the prisms are arranged as in Fig. 12 then the ray entering A takes the direction of an ordinary ray, like mor (Fig. 10), and is eliminated by the film of balsam. No light leaves the analyzer, and, accordingly, the field of vision appears dark. The same thing happens at a distance of 180. In all cases where the planes of polarization (or the principal 6 INTRODUCTION. sections) of the two Nicols are neither parallel nor at right angles to each other, the polarized light entering the analyzer is separated into an ordinary and an extraordinary ray, varying in intensity with the angle at which the planes of polarization of the two prisms are inclined to each other. Suppose them at first to be crossed, that is, set for darkness. Then, if we turn the analyzer through a small angle, the luminous intensity of the laterally-deflected ordinary ray will greatly exceed that of the transmitted extraordinary ray. Nevertheless, the latter suffices to slightly illuminate the field of vision. If the angle be increased to 45, the ordinary and extra- ordinary rays will be of equal intensity, so that the light leaving the analyzer will have exactly half the luminous power of the total entering light. By increasing the angle further, the luminous power of the transmitted ray will gradually exceed that of the eliminated ray, until at an angle of 90 the latter ceases altogether to exist, and the field of vision exhibits the maximum of brightness. Continuing the rotation in the same direction, we find another mini- mum of light at 180, and another maximum at 270. Fig. 13. 5. To observe these phenomena, the instrument shown in Fig. 13 may be used. The hori- zontal bar d, secured on a stand, carries at one end the fixed polar- izing Nicol ., and at the other the analyzing Nicol b, which, by means of the lever c 9 can be turned with its frame about its axis. In connection with the lever, a single or a double index moves round the divided disc, which is fixed to the bar. Be- tween the Nicols can be inserted the tube/) the ends of which can be closed with glass plates. We first direct the polarizer a towards some luminous source, and the phenomena are simplified by using monochromatic light, ?:, a Bun sen flame playing on a bead of common salt. The tubejis left empty or filled with water. INTRODUCTION. 7 Now, if we look through the analyzing Nicol while revolving it, we shall be able readily to find a position in which the field of vision appears darkest. Suppose the index now to be at the zero-point on the disc. Then, as explained above, on continuing the rotation we shall find, in a complete revolution, another maximum of darkness at 180, and the two maxima of light at 90 and 270 respectively. For purposes of scientific observation, the points of greatest darkness are to be preferred as marks of reference, since at these points the least movement of the Nicol produces a percep- tible change in the appearance of the field of vision. 6. Now, if the tube be filled with a solution of cane-sugar instead of water and put in its place, the analyzer having been previously set to darkness (0 or 180), it will be found that the field of vision now appears bright, and to obtain the maximum of darkness we must turn the analyzer to the right through a certain angle. If the plane of polarization of the fixed polarizer of the in- strument has the direction P P' (Fig. 14), so long as the tube is empty the rays cannot pass through the analyzer, since its plane of polari- zation A A is at right angles to P P'. But, if after the introduction of the sugar solution the field of vision exhibits the maximum of darkness when the plane of polarization of the analyzer is revolved into the position .', we are bound to conclude that the rays originally vibrating in the plane P P', in their passage through the solution, have experienced a certain deflection of their plane of vibration, and that their vibrations are now perpendicular to a a that is, they take place in the plane p p' . The angle a, through which the analyzer has to be turned to bring a recurrence of darkness in the field of vision, and which can be read off on the graduated rim of the disc, is called the angle of rotation, and is the measure of the deflection experienced by the plane of polarization. A number of other substances behave in the same way as cane- sugar that is to say, the analyzer requires to be turned to the right hand from zero to reach the point where the light vanishes. Again, if the tube be filled with nicotine or a solution of amygdalin, the phenomenon of reappearance of light occurs as before ; but, in this 8 INTRODUCTION. case, to set the instrument back to darkness the analyzer has to be turned to the left. These substances, therefore, cause a deflection of the plane of polarization to the left. This rotation of the plane of vibration, or of polarization, is called circular polarization. Substances which exhibit this power are said to be circular-polarizing or optically active, and are distinguished as right-rotating (dextro-gyrate) or left-rotating (Isevo-gyrate), whilst those substances which have not this power are said to be inactive. Circular polarization was first noticed in 1811 by Arago, in rock- crystal. In 1815 Biot discovered the optical activity of organic bodies, and in a series of important investigations, extending over more than forty years, he deduced the laws and explained the nature of the phenomena. His observations form the basis of our present knowledge of the subject. 1 1 Biot: Mem. de V Acad. 2, 41; 3, 177; 13, 39; 15, 93; 16, 299. Ann. Chim. Phys. [2] 9, 372; 10, 63; 52,58; 69, 22; 74,401; [3] 10, 5, 175, 307, 385 ; 11, 82; 28, 215, 351; 29, 35, 341, 430; 36, 357, 405; 59, 206. NOTE BY TRANSLATOR. For the sake of some readers, it may be as well to add here a rather more explicit account of the action of a piece of apparatus so fundamental in polariscopic work as the Nicol prism. Taking Fig. 10 in the text, let us add to the author's construction by drawing through tn a both- ways perpendicular (normal) to ab', as also through p and o similar normals to d' b'. Now, in their passage through the first half of the prism, the rays are both bent towards the normal in n\, (i.e., outward from the balsam), to extents due to their different refractive indices, the ordinary ray wn o (refr. ind. 1-66) more than the extraordinary ray mp (refr. ind. T52). The refractive index for Canada balsam for mean light being 1-54, the extraordinary ray on meeting the line b' d' (which, to represent a layer of sufficient thickness, must be broadened into a rhomboid) here encounters a medium of refractive power almost identical with that of the calc-spar which it left, so that this ray passes on with but a minute deviation inwards, due to the balsam being slightly more refractive than the spar for this ray. On the other hand, the balsam being very considerably less refractive than the calc-spar for the ordinary ray, causes that ray to diverge outwards from the normal, o n' 3 , and so much so, that it cannot hold a course through the balsam at all, but, inasnmch as the angle of incidence mon 3 in the more refractive medium exceeds the so-called critical angle, the ray suffers total refection from the surface, so that the angle ron 3 equals angle mo ?? 3 . The critical angle, or angle at which a ray, issuing from a more refrac- tive into a less refractive medium, emerges just parallel to the bounding surfaces, depends on the relative index of refraction. Simple geometrical considerations show that if the angle to the normal in the more refractive medium has a sine whose value is greater than the ratio of the absolute indices, the ray cannot emerge into the lees refractive medium. Now, in the case before us the ratio in question for balsam and spar is 1>54 = 0-928 = sin 68. 1-66 Hence the limiting value of m o w 3 , so that m o might just emerge in direction o d', is 68. If no w mo wore parallel to ad', the angle mon 3 would be just 68, being opposite to INTRODUCTION. 9 a b' ad', which has been ground down to 68 the figure mad'n z in that case forming a parallelogram. But in passing through the first half of the prism, the ray is refracted FIG. 10A. so that the angle mo>i 3 is always greater than b'a.d'. Thus we see that by grinding the end- faces of the prism so that b' ad' = 68, we secure that the angle mon 3 shall always exceed the critical angle, and the importance of this pro- cedure in the construction of the prism becomes apparent. As to what happens when a second Nicol is used to receive the extraordinary ray emerging from the first, the following consider- ations may perhaps be found useful : In all uniaxial crystals there are two directions at right angles to each other, the one of greatest resistance to the propagation of luminous vibra- tions, the other of least resistance. These planes are in the direction of the principal axis (see Fig. 5) and at right angles thereto. Calc-spar transmits only such light, the vibrations of which take place in either of these two directions ; and all incident light propagated by vibrations in a plane at any other angle to the principal section is resolved into two such component rays. But the velocities of transmission in the two directions are unequal ; that is, since amount of refraction depends on velocity of transmission, the refrac- tive index of the spar is, as we have already said, different in the two directions. Now if the second Nicol be arranged behind the first, so that corresponding planes in the two prisms be co- incident (as in Fig. 11), the extraordinary ray, coming into a plane of the same resistance as that which it left, is propagated with the same velocity as it had in the first prism, and is, therefore, similarly refracted, i.e., it takes a course similar to Itnpg (Fig. 10) in the first Nicol, emerging unaltered. If, however, the second prism be arranged so that corresponding planes shall cross, then the extraordinary ray, coming into a new plane in which it travels with greater velocity than before, is refracted accordingly, taking a course similar to Imor (Fig. 10) in the first Nicol, i.e., is totally reflected, so that no light emerges. Lastly, if the planes of the Nicols be crossed at any other angle, the light cannot pass in the plane it encounters in the second Nicol, but is resolved into two components in the two directions at right angles to each other, in which alone (as we have said) calc-spar transmits light-vibrations that component which takes the course of the principal section being eliminated by the Canada balsam, whilst that which takes a course at right angles thereto alone emerges. Now that reduction of intensity in luminous power which may be effected on a polarized ray emerging from one Nicol by opposing to its course an impassable plane of a second Nicol, is also effected by opposing to its course a rotatory substance. The ray is made to vibrate in a different plane ; in other % words, the plane of polarization is rotated, and the resulting phenomenon is the same as if the first Nicol had been rotated to the same extent. The physical explanation of this rotatory power is discussed in succeeding chapters. [D. C. B,.] II. GENERAL ASPECTS OF OPTICAL ACTIVITY. A. Classification of Active Substances. 7. Circular polarizing substances may be divided into two classes : (1) Bodies which only in a crystalline state possess the property of rotating the plane of polarization, and which lose this property entirely when brought (either by solution or fusion) into an amorphous condition. Up to the present, only a few such active crystalline substances are known. In the table annexed these substances are recorded, along with the angle a, through which the ray D, or mean yellow light j (jaune), is rotated on passing through a plate of each substance 1 millm. in thickness. Substances. Formula. a per 1 millm. Observer. Cinnabar HgS a D = 32-5 Descloizeaux Rock crystal Sodium chlorate . . SiO 9 NaC10 3 O D = 21-67 3-67 Biot, Broch, &c. Marbach ,, bromate . . NaBrO 3 aj = 2-80 , , periodate . . NaJ0 4 + 3H 9 23-3 Uliich, Groth Potassium dithionate K 2 S,0 6 a D = 8-39 Pape Strontium ,, SrSoO 6 + 4 HoO Oj 1-64 Calcium , , CaS;0 6 + 4K,O aj = 2-09 " Plumbic ,, PbS 2 6 + 4H~ 9 O 5-53 Sodium sulphantimoniate Na 3 SbS 4 + 9H 9 O Oj = 2-7 Marbach Uranium sodium acetate . (UrO) 2 .Na . 3 C;H 3 O 2 a j 1-8 Matico- camphor . . O TT O 2-4 Hintze Benzil C 1 4H 10 O 2 D = 24-92 Descloizeaux Ethylene-diamine sulphate G-uanidine carbonate Diacetyl-phenol-phtalein (N 2 H 4 . C.,H 4 )H 9 S0 4 (CH 6 N 8 ),". H,00, (C 20 H 13 4 )(C 2 H 3 0) 2 D = D = 14-35 19-7 v. Lang Bodewig CLASSIFICATION OF ACTIVE SUBSTANCES. 11 The crystals of these substances are, without exception, either single-refracting (regular) or uniaxial double-refracting (hexagonal or quadratic). In the latter, the optical power is only displayed in the direction of the principal axis, and we have therefore to use plates cut perpendicularly thereto. Moreover, every one of the above specified substances occurs both in right-rotating and left- rotating crystals, and the amounts of deviation are exactly the same for plates of equal thickness. Several of these substances quartz, sodium period ate, dithio- nates, guanidine carbonate, and matico-camphor, give external evidence of the possession of this property by the existence of hemihedral or tetartohedral faces, which are right-handed or left- handed according as the crystal rotates to the right or left. 8. (2) Bodies which display rotatory power when dissolved, and, consequently, in the amorphous state. The substances of this class are, without exception, carbon-compounds, and either occur naturally in vegetable or animal organisms, or as derivatives from these by simple metamorphoses. No inorganic substance is known which in solution exhibits rotatory power, and it would seem that this property is a peculiar attribute of the carbon-atom. The substances in this class are either right-rotating ( + ) only or left-rotating ( ) only, with the exception of a few which mani- fest the power in both directions. The subjoined table contains as complete a list as possible of all active substances known up to the present time, with their most important derivatives, and also, in the last column, a list of compounds which, although nearly related to these substances, are inactive : Substances. Lsevo-rotatory. Dextro-rotatory. Inactive. Sugars C 12 H 22 O n Cane-sugar, Milk- sugar, Mycose, Melitose, Melezi- tose, Maltose Synanthrose Sugars C 6 H 12 6 Laevulose In vert- sugar Inverted Synanthrose Sorbin Dextrose (Honey- sugar, Grape- sugar, Starch - sugar, Salicin-, Amygdalin-, Phlorhizin - sugar, Gum -sugar). " Galactose, Eucalyn Inosite 7 12 GENERAL ASPECTS OF OPTICAL ACTIVITY. Substances. Leevo-rotatory. Dextro - rotatory . Inactive. Mannite Group Mannite Lsevo-mannitan Mannitone Matezite Nitro-mannite Dextro -mannitan Nitro-mannitan Quercite Finite Iso-dulcite Bornesite Carbohydrates C 6 H 10 5 Inulin, Inuloid Gum Arabic Beetroot Gum Starch, Xyloidin Dextrin, Glycogen Gum Arabic Dextran (Fermenta- tion Gum) Mannitose Quercitose Sorbite Dulcite, Nitro-dulcite Erythrite Dambonite, Dambose Cellulose Nitro-cellulose Pectin Glucosides Amygdalin, Amyg- dalic Acid, Man- delic Acid Salicin, Populin Phlorhizin,Digitalin, Cyclamin, Coniferin Quinovin Apiin Glycyrrhizin Phloretin Tannic Acids? Acetyl derivatives of Inulin Gtimmic Acid Fermentation Amyl- alcohol Derivatives of the above Groups. Para -lactic Acid Salts and Ether Anhy- drides Acetyl derivatives of Dextrose, Milk- sugar, Mannite, Mannitan, Dulcite and Starch Glucosan, Saccharic Acid Amyl-alcohol from Dextro -amyl Chlo- ride Derivatives of LEBVO- amyl- alcohol (Di- amyl, Ethyl -amyl, Amyl chloride, io- dide and cyanide, Amy lamin e , Amyl - valerate, Valeric al- dehyde, Valerianic Acid, Capronic Acid) Para-lactic Acid Levulinic Acid Mucic Acid Fermentation Butyl - alcohol Octyl- alcohol from Bicinus Oil Methyl -amyl Amyl hydride Amylene from active Am y 1 - alcohol CLASSIFICATION OF ACTIVE SUBSTANCES. 13 Substances. Laevo -rotatory. Dextro - rotatory . Inactive. Laevo -tartaric Acid Dextro-tartaric Acid Para-tartaric Acid ,, Salts ,, Salts SyntheticTartaricAcid Laevo - tartramide Dextro - tartramide Pyro-tartaric Acid Meta- tartaric Acid Nitro- tartaric Acid Di- tartaric Acid Synthetic Malic Acid Natural Malic Acid Malic Acid from Dex- Maleic Acid tro - tartaric Acid Fumaric Acid Acid Malate of Am- or Asparagine Malate of Ammonia Succinic Acid Citric Acid monia in Water in Nitric Acid Citro- malic Acid Vegetable Acids and Allied Substances Malamide from Las vo - malic Acid NeutralMalates (Zinc- and Antimon- Am- monium Malates) in Water Asparagin inAqueous and Alkaline Solu- Asparagin in Acid Solutions tions Aspartic Acid in Al- Aspartic Acid in Acid Aspartic Acid from kaline Solutions Solutions Fumaric or Maleic Acid Glutaric * Acid Glutamic Acid Quinic Acid Quinovic Acid in Al- kaline Solutions Lactonic Acid Dextronic (Gluconic) Atractylic Acid Acid Lsevo-oil of Dextro -oil of Camphene Turpentine or Terebenthene Turpentine or Australene Camphilene Terebene (French, from (English orAmerican, Terebilene Pinus maritima ; f TomPinus balsamica, Polyterebenes Venetian, from Australis andTaeda; Terpinol P. Larix, German, from Templin-oil, from P. sylvestris, nigra, P.Picea or Pumilio). and Abies). Terpenes Terebenthene hydro - Australene hydro - /"** TT UIQ Xl 16 chlorate chlorate Terecamphene Liquid Terpinhy- Austracamphene drate Solid Terpinhydrate Iso -terebenthene Tetra-terebenthene Terpene from Parsley Terpene from Oils of Oil Lemon, Orange, and Poplar Cicutene .Oils of Copaiba, Cu- Anethol, Oils of Cas- Oils of Anise, Cassia, bebs, Lavender, carilla, Chamomile, Cloves, Cinnamon, Parsley, Rue, Roses, Coriander, Fennel, Gaultheria, Bitter Tansy, Thyme, Nutmeg, Myrtle, Almonds, Mustard, Juniper, andCrisped Sassafras Thymol Ethereal Oils mint The following a re both Dextro- and Lse vo- rotatory : Oils of Peppermint, Cu- min, Rosemary, Salvia, Savine, Elemi, Cas- carilla Probably this should be Glutanic acid (vide p. 232). [D. C. R. ) 14 GENERAL ASPECTS OF OPTICAL ACTIVITY. Substances. Lsevo- rotatory. Dextro - rotatory. Inactive. Sylvic Acid Pimaric Acid Guaiacum Acid Podocarpic Acid Dextro-pimaric Acid Euphorbone Camphors and Allied Substances Alkaloids Matricaria - camphor Menthol, Patchouli-, Blumea-(Ng ai)and Uubia - camphor Borneene Camphoric Acid, from Matricaria - camphor Camphoric Anhy- dride and Cam- phoronic Acid, from Dextro - camphoric Acid Carvol, from Crisped mint Oil Citronellol Ordinary Camphor Borneol, Amber- cam - phor, Pvosemary- ( Ledum) camphor Ethyl- and Amyl- camphor Camphor Bromide Camphoric Acid, from ordinary Camphor Camphic Acid Cymol, from Oil of Cumin and Cu- minol Carvol, from Cumin- oil Absinthol Myristicol Quinine, Cinchonidine Homocinchonidine Paytine, Cusconine Aricine Morphine, Codeine Narcotine in Alcohol Pseudomorphin e Thebaine, Papaverine Laudanine Strychnine, Brucine Nicotine Atropine Aconitine Geissospermine Quinidine (Conchi- nine), Quinicine, Cinchonine, Cincho- nidine, Quinamine Quinidamine,* Quinamicine , Diho - mo-cinchonicine * Apodiquinicine * Narcotine in Hydro- chloric Acid Laudanosine Conine Cicutine Pelosine (Buxine) Pilocarpine Lavandula - camph or Camphrene Sulpho-camphoric Acid All other Cymols Safrol Geraniol Meconine Narceine Hydrocotarnine Cryptopine Aribine, Betaine Paraconine Berberine Veratrine Emetine Piperine Sanguinarine Indifferent Substances Santonin Santonic Acid Picrotoxin Jalapin Hydrosantonic Acid Hgematoxylin Echicerin, Echitin Echitein, Echiretin Ostruthin Leucotin Oxyleucotin Hydroootoin CLASSIFICATION OF ACTIVE SUBSTANCES. 15 Substances. La3vo-rotatory. Dextr o - rotatory . * These are the names by which the three sub- stances are best known to English chemists ; but the author gives Hesse's names, viz., conchinamim, dihomo-cinchonine, and diconchinine respectively. For the last, apodiquinicine was suggested by Wright, on the ground of its greater resemblance to quinicine, of which it may be regarded as a first anhydride, thus : 2 (Co H 24 N 2 2 ) - H 2 = C 40 H 46 N 2 3 .-[I>.C.R.] Bile Constituents Cholesterin (Phytosterin) Glycocholic Acid Taurocholic Acid Cholalic Acid Choloidic Acid Hyoglycocholic Acid Hyocholoidic Acid Lithofellic Acid Gelatinous Substances. Gelatin, Chondrin Albumins Serum-albumin Egg-albumin Paralbumin Sodium- albuminate Casein, Syntonin Peptones According to the foregoing list, the number of natural active substances known amounts to about 140, of which 65 are left- rotating, 60 right-rotating, and 15 both right and left-rotating. Of active derivatives, counting all hitherto examined salts of the alkaloids and vegetable acids, there are at least as many known, thus bringing the total number of optically active carbon-compounds up to close on 300, and no doubt many other substances hitherto unexamined possess the power of rotating the plane of polarization. Substances which display the rotatory power when in a state of solution, and are crystallizable, are not found to exhibit optical activity in the crystalline state, as when a polarized ray is passed through plates cut from them. This is the case with cane- sugar, tartaric acid, asparagin, camphors, etc. (see Biot, 1 Descloi- zeaux 3 ), Now the phenomenon of circular polarization is only observable in single -refracting or in uniaxial double-refracting crystals, and in the latter only in the direction of the optic axis. But the substances just referred to are all biaxial, and thus in no direction single-refracting; consequently, circular double-refraction 31 could not in any case be observed in them, as it would be over- powered by the more marked phenomenon of ordinary double- refraction. Whether they are really inactive in the crystalline state is undecided. 1 Biot: Mem. de VAcad. 13, 39. 2 Descloizeaux : Pogg. Ann. 141, 300. 3 The expression refers to Fresnel's theory of circular polarization, in which the two rays are supposed to vibrate in opposite circular paths. See 12. [D. C. E,.] 16 GENERAL ASPECTS OF OPTICAL ACTIVITY, But when these substances are brought into the amorphous solid form their optical activity is retained a fact first observed by Biot with cast plates of sugar and tartaric acid. 1 9. As a third and distinct class are regarded those substances which are known to exhibit rotatory power both in the crystalline state and in solution. At present only two such substances are known, viz., strychnine sulphate crystallizing with water in quad- rate octahedra, 2 and regular amylamine-alum. 3 B. Nature of Rotatory Power. 10. The fact that substances in the first of the above classes manifest rotatory power only in the crystalline state and lose it directly they are brought into solution, is proof that the rotation is dependent^ on Crystalline structure that is, upon a particular arrangement in the groups of molecules (forming the crystal). Dissolution or fusion breaks up this arrangement, and the optical power is consequently lost. In this case then the phenomenon is purely physical. The second class of substances, on the contrary, exhibit rotatory power in the liquid state. Now there is every reason to believe of matter in this form that the smallest quantities, capable of independent motion as units consist, not of individual molecules, but of groups, and it may therefore be conjectured that the solution of a solid in a liquid does not entail a complete separation of the molecules from each other, but that they still exist in composite groups. 4 Whenever, therefore, we find liquids exhibiting rotatory power, we might assume that, as in the case of crystals, the cause lies in the mode in which the molecules group themselves. Thus again the phenomenon would be purely physical. But for this supposition to be correct the rotatory pro- perties of active substances should vanish when these group- ings are really broken up that is, when the substances are brought into the norma . gaseous state. This important point was first investigated by Biot, 5 in 1817. He filled a tin tube, fitted at both 1 Biot: Mem. de VAcad. 13, 126. Ann. Chim. Phys. [3] 10, 175; 28, 351. 2 Descloizeaux : Pogg. Ann. 102, 474. 3 Le Bel: Ber. d. deutsch. chem. Gesell. 5, 391. 4 See, on this point, Naumann : Tfeber Moleciilverbindungcn nachfesten Verhaltnissen Heidelberg, 1872, pp. 3749. 5 Biot : Mem de VAcad. 2, 114. NATURE OF ROTATORY POWER. 17 ends with glass plates, and 30 metres in length, with vapour of oil of turpentine, which he found had still the property of pro- ducing a certain amount of deviation in a ray of polarized light. Unluckily, before the observations were completed, the vapour accidentally caught fire, and the apparatus was destroyed. The experiment was next tried by D. Gernez, 1 in 1864, who, with the aid of instruments of a superior kind, determined the rotatory powers of various active substances at rising temperatures, and eventually in the gaseous state. The substances thus examined were orange-peel oil ( + ), bitter orange oil ( + ), turpentine oil ( ), and camphor ( + ). In each the specific rotation [a], that is, the angle of rotation calculated for equal densities, = 1, and equal lengths of layer = 1 decim. diminished as the temperature increased ; and when the same substances were tested in the gaseous state they gave a specific rotation merely reduced in proportion to the temperature to which they had been exposed. The table appended shows the results obtained with oil of turpentine and camphor : State of Aggregation. Temp. (Cent.) Density compared with water, d. Observed Angle of Rotation, a. Length of Tube in decim., 1. Specific Rotation M=J7i Oil of Turpentine (left-rotating). 11 0-8712 15-97 0-5018 36-53 Liquid 98 0-7996 14-47 0-50215 36-04 154 0-7505 13-50 0-50237 35-81 Vaporized 168 0-003987 5-76 40-61 35-49 Observed Density of Vapour at 168 Cent. = 4-981 Calculated = 4-700 Camphor (right-rotating). Melted Vaporized 204 220 0-812 0-003843 31-46. 10-98 0-5509 40-63 70-33 70-31 Observed Density of Vapour at 220 Cent. = 5-369 Calculated =5-252 It will be seen that the observed densities of the vapours used Gernez : Ann. Sclent, de V ecole norm, sup. 1,1. 18 GENERAL ASPECTS OF OPTICAL ACTIVITY. in the experiment agreed very nearly with their calculated densities. The polarized ray must therefore have been influenced almost entirely by individual molecules, not by groups. The rotatory power [a] was, however, manifested to its full extent, and the con- clusion is that here optical activity must be a property resident in the molecule itself, and dependent on its atomic structure. The phenomenon is thus seen to be really chemical. The optical activity of crystals and that of liquids are, therefore, wholly distinct phenomena, and to the latter Biot has given the name of moleculur rotation, indicating that it is a property resident in the individual molecule. 11. Magnetic Rotation. A rotatory movement of the plane of vibration of a ray of polarized light can be produced in all transparent isotropic bodies, solid or liquid (as glass, water, &c.), by placing them between the poles of a magnet, or within the helix of an induction-coil. This so-called magnetic rotation differs alto- gether from rotation as seen in naturally active substances. It lasts so long only as the electric influence is continued ; it varies in degree with the intensity of the latter ; and it takes a right- or left-handed direction, irrespective of the medium, according to the position of the poles of the magnet or the direction of the electric current. There is also this further characteristic difference between the two. Let a polarized ray be transmitted through a naturally active substance, which, for the sake of example, we will say is right-rotating. Then the deviation of the plane of polarization will always be such that, to follow the movement of the ray, the instrument must be turned towards the right of the observer that is to say, the direction of rotation, with reference to that of propa- gation of the ray, is invariable. If after passing through the refractive medium the ray is returned into it by reflection, and tbe analyzer brought round to the same side as the entering ray, it will be found that rotation is annulled. The rotation dependent on magnetism is of a quite different character. The ray transmitted, let us say, from south to north pole, in the direction of the observer, will appear deflected towards the right hand, and, trans- mitted from the opposite end of the tube, towards the left. If the ray transmitted from south to north pole be reflected back, it will appear farther deflected to the left, so that an analyzing Nicol placed to receive it must be rotated to the left through an angle NATURE OF ROTATORY POWER. 19 equal to double the previous angle of rotation. If again brought back to the north end by a second reflection, this third trans- mission of the ray through the refractive medium will carry the analyzer placed at the north end through an angle equal to three times the original angle of rotation, and so on. The same thing happens when circular polarization is induced by an electric current, the rotation always taking the direction of the induction -current from the observer's stand-point. Magnetic rotation, not being a property of the chemical mole- cule, need not be further discussed here. 12. The optical theory of circular polarization in quartz is due to Fresnel. 1 According to him there occurs in quartz, in a direction parallel to the main axis of the crystal, a peculiar kind of double refraction, whereby a linear polarized ray on entering is decomposed into two rays, each of which pursues a helical course, the one turning to the right, the other to the left. On emerging, the two circular-polarized rays unite into a single linear-polarized ray again, but if the velocities with which they have traversed the refractive medium have been unequal, the plane of vibration of the emergent ray will have a different direction to what it had originally. It will follow the hands of a watch that is to say, it will have rotated to the right if the circular-polarized ray turning in that direction has had the superior velocity, and vice versa. The existence of these divided rays in rock-crystal was experimentally established by Fresnel, and subsequently by Stefan, 2 and also by Dove, 3 who found that in coloured quartz (amethyst) they were unequally absorbed. The theory of circular polarization has since been treated mathematically by Clebsch, 4 Eisenlohr, 5 Briot, 6 v. Lang 7 and others. Regarding the structure requisite in a crystalline medium to produce rotation of the plane of polarization, a theory has been proposed of an unequal condensation in certain directions of the 1 Fresnel: Ann. Chim. Phys. [1] 28, 147; Wiillner's Lehrbuch der Pliys. 3 Aufl., 2, 589. 2 Stefan: Pogg. Ann. 124, 623. 3 Dove : Pogg. Ann. 110, 284. 4 Clebsch: Crete's Journ. f. Math. 57, 319. 5 Eisenlohr: Pogg. Ann. 109, 241. 6 Briot: Comptes Rend. 50, 141. 7 v. Lang: Pogg. Ann. 119. 74. Erg. Bd. 8, 608. C 2 20 GENERAL ASPECTS OF OPTICAL ACTIVITY. ether surrounding the molecules, considerable enough in reference to the wave-length of the transmitted ray, and conditioning, of course, a particular molecular structure of the substance. The connection between the direction of rotation and the appearance of right or left-handed hemihedric planes in active crystals has led to the supposition that their ultimate parts are superposed so as to form right-handed or left-handed helices. This view, suggested by Pasteur, 1 Rammelsberg, 2 and others, appears highly probable from experiments first instituted by Reusch, 8 and more recently further extended by Sohncke. 4 If a number (12 to 36) of thin laminae of optically biaxial mica be superposed in the form of a spiral, so that the principal section of each may form a certain angle (45, 60, 90, or 120) with that of the preceding one, an optical combination is produced, which causes rotation in a ray of polarized light precisely like an active crystal, the direction of the rotation being to the right or left hand according as the plates are arranged in a right or left-handed spiral. The optical properties of such mica-combinations were minutely investigated by Sohncke, who has arrived at the conclusion that, provided we use sufficiently thin laminae, we shall obtain combinations exhibiting rotation-phenomena more nearly obeying the laws found to hold good for quartz and other active crystals. Hence, Sohncke considers as, to say the least, probable, that rotatory crystals possess a structure analogous to that of these mica-combinations. 13. As to the constitution of active liquids, we are driven to seek for the peculiarity of structure on which their power of rotation depends in the arrangement of atoms in the molecule. Now, Pasteur" supposes that molecules like all other material objects may be divided, in respect of shape and the repetition of their symmetrical parts, into two great classes, viz.: 1. Those whose images are superposable by the bodies themselves (as straight flights of steps, dice, &c.). 2. -Those whose images are not superposable (as winding stairs, screws, irregular tetrahedrons, &c.), and which may possess 1 Pasteur : Recherches sur la dissymetrie moleculaire de* prodmts organiques nature!-*. Lemons de Chimie professces en 1860. Paris, 1861. 2 Eammelsberg : Ber. d. deutsch. chetn. Gesell. 2, 3i. a Reusch : Pogg. Ann. 138, 628. 4 Sohncke: Pogg. Ann. Erg. Bd. 8, 16 5 Pasteur: ReehercJies, &c. p. 27. NATURE OF ROTATORY POWER. 21 either of two structurally opposed (or enantiomorphous) shapes. Molecules of the former class possess symmetry of structure ; those of the latter class have their atoms disposed asymmetrically, and accordingly exhibit optical activity. In 1848, Pasteur 1 made the important discovery that inactive para-tartaric acid is separable into right-rotating and left-rotating tartaric acids; and the sodium- ammonium salts of these two acids are distinguishable from each other by the presence of dextro-hernihedric and bevo-hemihedric planes respectively. Moreover, these salts retain their opposite characters in solution, by exhibiting opposite rotatory powers. Hence we may suppose that the property of asymmetrical structure of opposite kinds, such as we have seen in crystals, may occur in molecules also, and the precise nature of the arrangement of the atoms, or rather atom-groups, may reasonably be assumed to be here also of a helical kind. Whether the phenomenon of circular double- refraction, as exhibited by crystals, occurs also in active liquids is still an undecided point, several experiments made by Dove 3 on sugar solutions and on oil of turpentine having led to no conclusive result. Hence, according to Pasteur's 3 views, the different optical modifi- cations of tartaric acid may be explained on the supposition that in dextro-tartaric acid the atoms which go to form the molecule are grouped in right-handed helices, whilst in laevo-tartaric acid they are grouped in helices, equal in size, but left-handed in direction : and hence, too, the inactivity of racemic (para-tartaric) acid on the ground of its being formed by the union of equal molecules of the two former modifications. But besides these, other forms are well known, optically inactive, but not separable into the two optically active acids. To explain the existence of these, some other assump- tion is necessary, either that the helical structure is in their case abolished (untwisted), as Pasteur suggests, or that their inactivity arises from compensation within the molecule which is composed of two atom- groups possessing opposite rotatory powers. As to chemical structure, however that is, the distribution of affinities between the atoms they do not differ from the other isomeric acids. Analogous optical modifications have been observed in a few other substances, which have been brought together in the table on page 22. 1 Pasteur: Ann. Chim. Phys. [3] 24, 442 ; 28, 56 ; 38, 437. 2 Dove: Pogg. Ann. 110, 290. 3 Pasteur: Recherches, &G. p. 38. 22 GENERAL ASPECTS OF OPTICAL ACTIVITY. ACTIVE. INACTIVE. Dextro-rotatory. Lsevo-rotatory. By Combination of equivalent Molecules of right and left-handed Modifications. By Difference in the Atomic Structure of the Molecule. Dextro-tartaric Acid Lsevo- tartaric Acid Para-tartaric Acid Meso-tartaric Acid Malic Acid from Dextro - tartaric Acid 1 Natural Malic Acid Malic Acid from Para-tartaric Acid 1 Malic Acid from Succinic Acid Laurel or ordinary- Camphor Matricaria Camphor Racemoid [or Para] Camphor 2 Camphoric Acid from Laurel Camphor Camphoric Acid from Matricaria Camphor < Para - camphoric Acid from Para Camphor or La- vender Camphor Meso - camphoric Acid 3 Similar conditions are found to exist in other substances, with the difference that the two oppositely active isoraers exhibit unequal rotatory powers. Thus, the following occur in dextro-rotatory ( + ), laevo-rotatory ( ), and inactive (0) forms: glucose (as dextrose + , laevulose , and glucose obtained by heating cane-sugar with water to a tempera- ture of 1 60 Cent., 0) ; terpenes (australene, the English oil of turpen- tine + , terebenthene, the French oil , terebene 0) ; amyl- alcohol (that formed from the laevo-alcohol by conversion into the chloride and reconversion into alcohol +, fermentation-amyl-alcohol , and the modification obtainable from either by distillation with caustic potash 0). See Le Bel 4 ; Balbiano. 5 In many substances one of the two active modifications is un- known. For example: ethylidene-lactic acid (from muscle juice -f, by fermentation or synthesis 0) ; cymol (from oil of Roman cumin -f , 1 Bremer: Ber. d. deutsch. chem. Gesell. 1875, 1594. 2 Chautard: Comples Rend., 38, 166; 56, 698. Erdmann : Journ. fur prakt. Chem. 90, 251. 3 Chautard: Jahresb. fur Chem. 1-863, 394; Jungfleisch : Jahresb. fur CJiem. 1873, 631. Wreden : Liebufs Ann. 167, 302. 4 Le Bel: Bull. soc. chim. [2] 25, 545. 5 Balbiano : Jahresh. fur Chem. 1876, 348. NATURE OF ROTATORY POWER. 23 synthetic cymols 0) ; mandelic acid (from amygdalin , from benzoic aldehyde 0) ; aspartic acid (from active asparagin in acid solutions +, from fumaric or maleic acids 0). Lastly, in a few substances the inactive form is still unrecog- nized, as, for example, in borneol (as dryobalanops camphor + , as blumea (Ngai) camphor, and camphor from fermentation of madder- sugar ) ; carvol (from cumin-oil and dill-oil +, from mint-oil ). See Fliickiger. 1 A whole series of ethereal oils exist in both dextro- rotatory and laevo-rotatory modifications. Optically different modifications of particular substances are found, in some cases, to exhibit differences in their other properties. Thus, the salts of active para-lactic acid are distinguished from those of inactive fermentation-lactic acid by different amounts of water of crystallization and somewhat different degrees of solubility (Wislicenus). Para-tartaric acid is more difficult of solution than the active tartaric acids. In their behaviour with inactive substances, Pasteur finds no difference between dextro- and laevo-tartaric acid ; thus their potassium, sodium, and ammonium salts, tartar emetics and tartramides exhibit no difference beyond opposite rotatory powers and the occurrence of incongruous hemihedry in the crystals. But it is otherwise when the two acids are allowed to react with active substances, as asparagin, quinine, strychnine, sugar, &c. Where combination takes place the compounds formed differ from each other in crystalline form, specific gravity, water of crystallization, and in the readiness to decompose under the action of heat. Dextro- tartaric acid forms with asparagin a highly crystallizable substance, laevo- tartaric acid does not : Isevo-acid malate of ammonia combines with dextro-acid tartrate of ammonia to form a crystallizable double salt, but not with the laevo- tartrate : laevo- tartrate of cinchonine is more difficultly soluble in water than the dextro-tartrate : dextro-tartrate of ammonia is decomposed by fer- ment-action, whilst laevo-tartrate undergoes no fermentation, and laevo- tartaric acid can, in consequence, be obtained in this way from para-tartaric acid, and so on. 2 To illustrate these peculiarities, Pasteur suggests the case of two screws one right-handed, the other left-handed driven into separate pieces of wood. When the fibres of the wood are rectilinear (inactive substance), two systems of the same kind will be produced ; but this will no longer be the 1 Fliickiger : er. d. deutaeh. chem. Gesell. 1876, 468. 2 Pasteur : Comptes Rend. 46, 61.5. 24 GENERAL ASPECTS OF OPTICAL ACTIVITY. case when the fibres are themselves arranged helically, and especially when the helices take opposite directions in the two pieces. Incongruous hemihedric faces are found in most crystallizable active substances. Pasteur 1 has observed them not only in the tartaric acids, tartrates, tartramides, and amic acids, but also in the crystals of acid malates of lime and ammonia, valerianate, and chloride of morphine, &c. In other cases, however, they are absent, as in active amyl- sulphate of barium. 3 Incongruous hemihedry, moreover, is found to occur in some crystals exhibiting no rotatory power, as formiate of strontium and magnesium sulphate. 3 The two charac- teristics are, therefore, not inseparable. C. Dependence of Optical Activity upon Chemical Constitution. 14. On this question Hoppe-Seyler 4 and also Mulder, 5 pro- ceeding on the ground that the rotatory properties of natural organic substances appear to be to some extent inherited by their derivatives, have expressed an opinion that optical activity is not dependent on the whole atomic structure of the molecule, but only on a particular part of it. The original compound they assume to include one or more active radicles, which in the derivatives may either appear unchanged or transformed into new but still active groups, or are eliminated altogether. A theory has lately been proposed by Le Bel, 6 and nearly at the same time by van't Hoff, 7 which is much more plausible, and inas- much as it brings into direct connection the rotatory powers and the constitutional formulae of substances, is of special significance to chemistry. Le Bel first suggested, that when a carbon-atom occurs in combination with four different radicles, a molecule of asymmetrical shape is constituted, which, as such, should exhibit rotatory proper- ties. Yan't Hoff, proceeding on a hypothesis of his own respecting 1 Pasteur: Ann. Chim. Phys. [3] 38, 437 ; 42, 418. Comptes Rend. 35, 176. 2 Pasteur : Comptes Rend. 42, 1259. 3 Pasteur: Ann. Chim. Phys. [3] 31, 67. 4 Hoppe-Seyler: Jo urn. fur prakt. Chem. 89, 274. 5 Mulder: Zeitsch. fur Chem. 1868, 58. 6 Le Bel: Butt. Soc. Chim. [2] 22, 337 (1874). 7 J. vaii't Hoff : Bull. Soc. Chim. [2] 23, 295 (1875). La chimie dans Vespace. Rotterdam, 1875. German ed. by F. Hermann, Die Lager ung der Atotne im Raum. Braunschweig, 1877. DEPENDENCE OF OPTICAL ACTIVITY UPON CHEMICAL CONSTITUTION. 25 the ultimate arrangement of atoms in space, was led to the same idea, in the working out of which a quite new stand-point has been reached in the subject of optical activity, as to the number of possible active and inactive isomers. This may briefly be explained as follows : Let us suppose a substance formed on the type CE 4 to be represented by a tetrahedron, in which the carbon-atom occupies the centre, and one of the radicles (simple or compound) combined with it, each of the four summits. It follows that when the radicles are all different, and exhibit different affinities for the central carbon- atom, their proximity to the latter will also be different. Such a combi- nation CRjUgRgR^ corresponds to an irregular tetrahedron destitute of planes of symmetry, and may always exist in two enantiomorphous forms. These two tetrahedrons will each exhibit, with reference to an axis parallel to a given side, a helical arrangement of the four summits, following a right-handed direction in one and a left-handed direction in the other. Such a carbon- atom, in combination with four different radicles, which van't Hoff denotes by the term asymmetrical, admits the possibility of two modifications of optical activity, the rotatory powers being equal in degree but manifested in opposite directions. In substances possessing two such asymmetrical carbon-atoms, and having their molecules composed of two similarly formed atom- groups, we may have, according as the groups themselves possess like or opposite activities, not only right- and left-handed modifications of the compound, but also an inactive form resulting from intra-molecular compensation. Of this we have an instance in the case of the tartaric acids (COOH . CHOH) (CHOH . COOH). If the number of asym- metrical carbon-atoms be further augmented, we shall obtain from the combined effect of the several atom-groups, partly positive and partly negative in their action, a still larger series of differently active modifications, consisting of pairs having equal but opposite activities ; the existence of several inactive forms becomes at the same time possible. (Bodies of the mannite group, glucoses, &c.) If we consider the chemical formulae of active compounds, the chemical constitution of which is known, we shall find that these always contain one or more asymmetrical atoms of carbon, and that no active organic substance can be adduced in which such atoms are wanting. On the other hand, we find that there exists a large number of substances, containing asymmetrical carbon-atoms, in which the power of optical rotation has not been observed, and it becomes a 26 GENERAL ASPECTS OF OPTICAL ACTIVITY. question how this absence of power is to be accounted for. The following suggestions are made by van't Hoff : 1. When such substances have a symmetrical chemical constitu- tion, the occurrence of internal compensation (as already mentioned) may explain their inactivity (as in erythrite, dibromo-succinic acid, &c.). 2. The inactive substances in question may in reality be com- pounds or mixtures of two isomers, with rotatory powers of equal intensity but opposite directions (para-tartaric acid), and in many cases these isomers, owing to the similarity of their other properties, are difficult to distinguish from one another, and have not yet been separated. In forming artificially substances containing asymmetrical carbon, it is probable that an equal number of molecules of the right-rotating and left-rotating modifications is always produced. 3. Many substances have not, up to the present time, been sub- jected to optical examination, or have been examined in a very super- ficial manner, and it is possible that owing to feebleness of action, inherent in or caused by the difficultly soluble nature of the substances, their rotatory powers may have been overlooked. (Mannite, for instance, which at one time was regarded as inactive, has lately been shown by Bouchardat 1 and by Yignon 2 to possess rotatory power.) To test as fully as possible the value of van't Hoff s hypothesis of the connection between asymmetrical carbon-atoms and the occurrence of optical activity, the following tabular arrangement has been prepared. The substances are grouped as follows : a. A list of active substances containing asymmetrical carbon- atoms, the latter being indicated by the prefix *. b. A list of substances closely related to the above, but which are inactive and contain no asymmetrical carbon-atoms. c. A list of substances containing asymmetrical carbon -atoms, but which, so far as is known at present, exhibit no optical activity. The formulao have been expressed so as to show the similarity or otherwise of the four radicles in combination with the centrical carbon-atom. 1 Bouchardat: Comptes Rend. 80, 120; 84, 34. 2 Vignon : Comptes Rend. 78, 148. DEPENDENCE OF OPTICAL ACTIVITY UPON CHEMICAL CONSTITUTION. 27 a. Ethylidene- lactic Acid C 3 Group. Active. (C H 3 ) *C H (0 H) (C 0.0 H). Inactive. b. Ethylene- lactic Acid Propionic Acid Glycerine Tartronic Acid Malonic Acid (CH 2 .OH) (CH 3 ) (CH 2 .OH) (CO. OH) (C . O H) c. Propylene-glycol (C H 3 ) Glyceric Acid (C H 2 . O H) a-Bromo-propionic Acid (C H 3 ) /8-Dibromo-propionic Acid (CH 2 Br) Propylene-dichloride (C H 3 ) Propylene-chlorhydrin (CH 3 ) CH (CO.OH). CH 2 (CO.OH). CH(OH) (CH 2 .OH). CH(OH) (CO.OH). CH 2 (CO.OH). *CH(OH) (CH 2 .OH). *CH(OH) (CO.OH). *CHBr (CO.OH). *CHBr (CO.OH). *CHC1 (CH 2 C1). *CH(OH) (CH 2 C1). C 4 Group. Active. Tartaric Acid (CO.OH) *CH (OH) [*CH (OH) (CO.OH)]. Tartramide (C O . N H 2 ) *CH (OH) [*CH (OH) (CO.NH 2 )]. Malic Acid (CO . OH CH 2 ) *CH(OH) (CO.OH). Malamide (C . N H 2 C H 2 ) *C H (0 H) (C . N H 2 ) . Asparagin (C . N H 2 C H 2 ) *C H (N H,) (C O . H). Aspartic Acid (CO.OH CH 2 ) *CH(NH 2 ) (CO.OH). Inactive. b. Succinic Acid Normal Butyric Acid Iso- butyric Acid Butyramide Fumaric Acid (CO.OH) (CH 3 -CH 2 ) (OH 8 ) (CH 3 -CH 2 ) (CO.OH) c. Erythrite (C H 2 . O H) Monobromo-succinic Acid (CO.OH) Dibromo-succinic Acid (CO.OH) Dimethyl-succinic Acid (CO.OH) Pyro-tartaric Acid (CO.OH) Secondary Butyl -alcohol (C H 3 ) /8-Butylene aiycol (CH 3 ) o-Hydroxy-butyric Acid (C H 3 C H 2 ) 0-Ditto ' ditto (CH 3 ) Aldol (CH 3 ) Chlorobutyl- aldehyde (C H 3 C H 2 ) Normal Butylene Dibromide (CH 3 -CH 2 ) CH 2 (CH 2 CO.OH). CH 2 (CO.'OH). CH(CH 3 ) (CO.OH). CH 2 (CO.NH 2 ). CH= (CH C O.OH). *CH (OH) [*CH (OH) - (CH 2 . OH)]. *CHBr (CH 2 CO . H). *CHBr [*CHBr (CO.OH)]. *CH (CH 8 ) [*CH (CH 3 ) (CO . OH)]. *CH(CH 3 ) (CH 2 CO.OH). *CH(OH) (CH 2 CH 3 ). *CH(OH) (CHo CH 2 .OH). *CH(OH) (CO'OH). *CH(OH) (CH 2 CO.OH). *CH(OH) (CH 2 CHO). *CHC1 (CHO)." *CHBr (CH 2 Br). 28 GENERAL ASPECTS OF OPTICAL ACTIVITY. C 5 Group. Active. a. Active Amy 1- alcohol (C H 3 C H 2 ) *C H (C H 3 ) (C H 2 . H) . , , Valerianic Acid (C H 3 C H 2 ) *C H (C H 3 ) (C . O H) . Oxy-glutaric Acid (C . H C H 2 C H 2 ) *C H (O H) (C . H). Glutamic Acid (C . O H C H 2 C H 2 )" *C H (N H 3 ) (C O . H). Inactive. b. 1 . Primary Isoamyl- alcohol (C H 3 C H . C H 3 ) C H 2 (C H 2 . H) . Tertiary Isoamyl -alcohol (C H 3 C . H . C H 3 ) C H 2 " (C H 3 ) . Iso- valerianic Acid (C H 3 C H . C H 3 ) C H 2 (C . H) . Oxypyro-tartaricAcid (CO . OH CH 2 ) C H . (0 H) (C H 2 C . O H). Citric Acid (CO.OH CH 2 ) C (OH) (CO . OH) (CH 2 CO.OH). c. 1. Sec. Normal Amyl- alcohol (C H 3 C H 2 C H 2 ) *C H (0 H) (C H 3 ) . Sec. Isoamyl- alcohol (C H 3 C H . C H 3 ) *C H (0 H) (C H 3 ) . Isoamylene-glycol (C H 3 C H . C H 3 ) *C H (0 H) (C H 3 H) . a - Hy droxyiso - valerianic Acid (CH 3 CH . CH 3 ) *CH (OH) (CO.OH). Ethometh-oxalic Acid (C H 3 C H 2 ) *C (0 H) (C H 3 ) (C . H) . C 6 Group. Active. a. Active Capronic Acid (C H 3 C H 3 C H 2 ) *C H (C H 3 ) (C . H). Mannite CH a . OH (*CH. OH) 4 CH, . OH. Dextrose C H 2 . H (*C H . O H) 4 C HO. Saccharic Acid CH 2 . OH (*CH. OH) 4 CO.OH. Dextrin 1 CH 2 OH *CH . OH *CH . OH *CH *C H CH 0. Appended we may place : *CH *CH.OH *CH.OH -*CH.OH CH 2 .OH. Cane Sugar 1 _ *CH *C(OH)(CH 2 OH) *CH.OH CH 2 .OH. CH *CH *CH.OH *CH.OH *CH.OH CH 2 .OH. Milk Sugar 1 O *CH *CH.OH C(OH)(CH 2 .OH) 2 . O 1 Fittig: Zeitsch.f. Riibenzucker-Ind. 1871,288. DEPENDENCE OF OPTICAL ACTIVITY UPON CHEMICAL i Inactive. b . Normal Caproic Acid (C H 3 C H 2 C H, C H>) C H 2 (C O . Iso-caproic Acid (C H 3 ) -CH (C H,) - (CH 2 C H 2 - C O . O H). Diethyl-acetic Acid . (C 2 H 5 ) C H (0, H 5 ) (C O . O H) . c. Methylisopropyl-acetic Acid (C H 3 C H . C H 3 ) *C H (C H 3 ) (C . O Hj . LeucicAcid (CH 3 CH . CH 3 C H 2 ) *CH (OH) - (C O . OH). The substances in C T and C 2 Groups are all of them inactive, though many possess asymmetrical carbon-atoms, as the following : Sodium Nitroethane *C . H . Na . (N 2 ) . (C H 3 ). Aldehyde Ammonia 1 *C . H . (O H) . (N H 2 ) . (C H 3 ). Chloral Sulphydrate *C . H . (O H) . (C C1 3 ) . (S H). Alcoholatei *C . H . (O H) . (C C1 3 ) . (0 . C, H 6 ). , , Hydrocyanide *C . H . (O H) . (C C1 3 ) . (C N) . Bromoglycollic Acid *C . H . (0 H) . Br. (C . O H). Hydrogen Silver-fulminate *C H . Ag . (N 3 ) . (C N). Ethylidene lodo-bromide C H 3 *C . H . J . Br. Ethylidene Methethylate C H 3 *C . H . (0 . C H 3 ) . (O .C 2 H 5 ) . Ethylidene Chloracetate C H 3 *C . H . Cl. (0 . C 2 H 3 0) . Ethylidene Chlcro-sulphonic Acid CH 3 *C . H . Cl. (SO 2 H). Ethylidene Oxychloride C H 3 *C . H . Cl. (0 *C H Cl C H 3 ) . In aromatic substances precisely similar conditions may be observed as in the fatty series. All ordinary benzene derivatives, in which the three double bonds of the C 6 nucleus remain intact, and which, in consequence, contain no asymmetrical carbon, are inactive. On the other hand, when one or more of these bonds are broken, the occurrence of asymmetrical carbon-atoms becomes possible. Where these are present the rotatory power will appear in some of the sub- stances, as we find it does in turpentine-oil, camphor, borneol, campholic acid, camphoric acid, &c., while in others it may be wanting, as in benzene dichloride, benzene tetrachloride, dihydrophthalic acid, c. Thus: a. Active (with asymmetrical C). Camphor. Camphoric Acid. C 3 H 7 C 3 H 7 *C H C H CH., / C CH S 1 These two substances, in the form of highly concentrated solutions in tubes one metre long, I have found to produce no perceptible deviation of the plane of polariza- tion. As regards the others no experiments have been recorded, but there can be no question that they are, like all artificial substances, beyond doubt inactive. 30 GENERAL ASPECTS OF OPTICAL ACTIVITY. b. Inactive (without asymmetrical C). Bitter Almond Oil. Resorcin. CHO A CH IT HC c. Inactive (with asymmetrical C). Benzene dichloride. Dihydrophthalic Acid. CH CH ,/\. V CH CH HC HC 'CHC1 I*CHC1 HC *C H (C . O H) *C H (C O . H) The active terpenes, C 10 H 16 cannot be formulated as No. I. of the annexed formulae, since it contains no asymmetrical C-atom, but onlv as either II. or III. Lastly, the asymmetrical carbon-atoms may be found in a lateral series, and then, as before, we get compounds, some active, some inactive, as the following : Active. Mandelic Acid (C 6 H 5 ) *C H (O H) (C . H). DEPENDENCE OF OPTICAL ACTIVITY UPON CHEMICAL CONSTITUTION. 31 Undetermined. Phenyl-lactic Acid (C 6 H 6 . C H 2 ) *C H (O H) (C O . H) . Tropaic Acid (C 6 H 5 ) *C H (C H 2 . H) (C . H) . Inactive. Benzoin (C 6 H 5 . C 0) *C H (0 H) (C 6 H 5 ) . Cinnamic Acid dibromide (C 6 H 5 ) *C H Br [*C H Br (C 6 H 5 )] l Diphenyl-succinic Acid (C 6 H 6 ) *C H (C . H) [*C H (C . H) C 6 H 6 ]. By comparisons of this kind, which might easily be extended, we find that up to the present no substance can be indicated with certainty 2 as disproving van't HofFs theory or the following state- ments based thereupon : 1. That optically active substances invariably contain one or more asymmetrical carbon-atoms. 2. That substances containing no asymmetrical carbon-atoms exhibit no optical activity. On the other hand, as van't Hoff has pointed out, and as may be seen from the above examples, the converse is not necessarily true, that " bodies containing asymmetrical carbon-atoms are always optically active." There are, in fact, numerous substances which contain asymmetrical carbon-atoms and yet exhibit no optical activity, and further research is needed to decide whether or not this inactivity can be referred to the causes before specified. But, even should further inquiry prove that asymmetrical carbon-atoms are not the sole condition but merely one of the conditions of optical activity, the foregoing statements, unless disproved by fresh discoveries, remain of great importance to chemistry, as they not only afford some sort of control over active substances, but may also yield definite indications as to the proper structural- formulae. 15. Artificial Production of Active Substances. The carbon- compounds in which optical activity has hitherto been observed, are all of them found in vegetable or animal organisms or as derivatives from these by simple decomposition. Many of these substances can be prepared artificially, but even when all the chemical attributes, 1 Presumably this should stand (C 6 H 5 ) *C H Br [*C H Br C . O H], the formula in the original being that for stilbene dibromide. [D.C.R.] 2 The activity observed by Berth elot (Comptes Rend. 63, 818; 85, 1191) in styrol and metastyrol, C 6 H 5 . C H = C H 2 , obtained from liquid storax, which substances contain no asymmetrical C-atoms, is referred by van't Hoff (Ber. d. deutsch. chem. Gesell. 1876, 5) to the presence of another substance, probably corresponding to the formula C 10 H 18 O. In like manner, the supposed optical activity of iodide of trimethylethyl- stibin is attributed to chemical impurity. Le Bel (Bull. Soc. Chlm. 27, 444). 32 GENERAL ASPECTS OF OPTICAL ACTIVITY. and, consequently, the chemical constitution of such compounds, agree with those of the natural substances, a difference is never- theless found to exist in their optical properties. Direct synthesis of substances from inactive components has hitherto resulted in the production of inactive modifications only. As already indicated, this inactivity of artificial substances may be apparent (i.e. latent) only and dependent on the following causes, which at the same time indicate the means to its possible removal : 1. In synthesis, it is probable that an equal number of dextro-rotatory and laevo-rotatory molecules may always be formed, which mix or combine together and so produce optical neutrality. As an instance of the kind, Jungfleisch 1 has shown that by converting ethylene through the intermediate products ethylene bromide, ethylene cyanide, succinic acid, and dibromo-succinic acid into tartaric acid, the inactive form is obtained, which by crystallization of its sodium- ammonium salt may be separated into dextro-tartaric and laevo-tartaric acids. This, at present, is the only instance that can be alleged of an artificial active substance ; and even here it must be observed that the direct result of the synthesis, the para-tartaric acid, exhibits no optical power. 2 As the physical and chemical properties of such opposite-rotating modifications may differ but little, they cannot in general be separated without great difficulty, and the more so, when they form not merely mechanical mixtures but true chemical combinations, as is the case with para-tartaric acid. Indeed the only substance as yet, whose inactivity depends on neutralization, which has been separated into right- and left- rotating modifications is para-tartaric acid. The separation can be effected by one of the following methods : a. By crystallization of the sodium-ammonium salt, and separa- tion by selection of the crystals with dextro-hemihedric from those with laevo-hemihedric planes (Pasteur 3 ). This method has been somewhat simplified by Gernez, 4 who found that by bringing into contact with a supersaturated solution of para-tartrate of sodium and 1 Jungfleisch: Bull. Soc. Chim. [2] 19, 194. Comptes Rend. 76, 286. 2 Pasteur (Comptes Rend. 81 , 128) rejects the instance unconditionally ; he maintains that up to the present time no active substance has been derived from inactive sub- stances, and that, therefore, optical activity affords a definite distinguishing charac- teristic between natural and artificial substances. 3 Pasteur: Ann. Chim. Phys. [3] 24. 442 ; 28, 56 ; 38, 437. 4 Gemez: Liebig's Ann. 143, 376. DEPENDENCE OF OPTICAL ACTIVITY UPON CHEMICAL CONSTITUTION. 3& ammonium a crystalline fragment of the dextro-tartrate, the latter alone crystallizes out, the laevo- tartrate remaining in solution, and vice versd. b. By causing the para-tartaric acid to combine with some other active substance, whereby two modifications with unequal solubilities are produced. Thus if cinchonicine (dextro-rotatory) be dissolved in para-tartaric acid, Isevo-tartrate of cinchonicine separates out first on evaporation. On the other hand, from a solution of quinicine (dextro-rotatory) in para-tartaric acid, crystals of the dextro-tartrate of quinicine are first separated (Pasteur). 1 c. By mixing a solution of para-tartrate of ammonia with ferment (yeast-extract), the dextro-tartrate is eliminated by fer- mentation, while the Isevo-tartrate remains unchanged (Pasteur). 2 Mixtures of right- and left-rotating molecules are probably pro- duced in the synthesis of all substances containing asymmetrical carbon, the molecules of which are not made up of two similarly constituted parts. This is probably the case with the malic acid obtained from monobromo-succinic acid, CO.OH CH 3 CH. OH CO . OH, with ethylidene-lactic acid from propionic acid, C H 3 CH . OH CO . OH, with mandelic acid prepared by treating benzoic aldehyde with prussic and muriatic acids, C 6 H 5 C H . OH CO . OH, &c. These products are all inactive, whereas the malic acid of plants, the ethylidene-lactic acid of muscle juice, and mandelic acid obtained by decomposition of active amygdalin with muriatic acid, despite the similarity of chemical constitution, all exhibit rotatory power. No attempts to dissociate any of these inactive preparations have yet been made. 2. The molecule produced by synthesis may be inactive by virtue of internal compensation that is, it may be made up of equal halves with opposite rotatory powers. In such cases it may reasonably be expected that optical inactivity will disappear when the symmetry of the molecule is disturbed, as for instance, in the case of inactive indivisible tartaric acid, by converting it into benzo- tartrate of ethyl or simply into an acid tartrate, thus: CO.OH CO.OC 2 H 5 CO.ONa CH.OH CH.OC 7 H 5 CH.OH CH.OH CH.OH CH.OH CO.OH CO.OC 2 H 5 CO.OH Tartaric Acid. Benzo- tartrate of Ethyl. Acid Tartrate of Soda. 1 Pasteur : Comptes Rend. 37, 162. 2 Pasteiir : Comptes Rend. 46, 615. D 34 GENERAL ASPECTS OF OPTICAL ACTIVITY. In these derivatives the halves being dissimilarly constituted, there ought to be rotatory power. Experiments in this direction have not yet been made, and it is quite possible that even such deri- vatives may prove inactive. This might easily be the case if the substitution took place in the right-rotating and left-rotating groups respectively of the two halves of the molecule, the result being an optically neutral mixture. Substances containing several asymmetrical C-atoms are, ac- cording to van't HofPs view, capable of forming by partial internal compensation certain isomers, with very feeble rotatory powers. Such a substance is mannite, C H 2 . OH-(*CH . OH) 4 -CH 2 . OH, which exhibits an extremely slight laevo-rotation. Converted into mannite dichlorhydrin, mannite hexacetate, mannite hexanitrate or into mannitan we obtain strongly dextro-rotatory substances. 1 By con- version, for example, into hexanitrate (nitro-mannite), C H 2 . . N 2 -(*CH.ON0 2 ) 4 -CH 2 .0.]S"0 2 , the symmetry of the chemical formula is not destroyed, but some alteration apparently takes place in the four asymmetrical groups, whereby they, or at any rate three of them, assume the right-rotating position. In this way Miintz and Aubin 3 converted an inactive substance, viz., the glucose obtained by exposing cane-sugar with a little water to a temperature of 160 Cent., into an active substance, by trans- forming it first into mannite (with sodium-amalgam and water), and then into nitro-mannite. So, likewise, inactive dulcite exhibits rotatory powers when converted into the diacetate, or into dulcitan d;acetate (Bouchardat). 3 3. Some of the resulting products do possess rotatory power, but only of a very feeble kind ; thus, for example, in the case of mannite, a layer 3 to 4 metres in depth is requisite for its determination. In such cases aid may be furnished by an observation of Biot, who found that the rotation of tartaric acid was considerably increased by the addition of boric acid. Similar results have been observed in other substances. Thus, Yignon 4 1 Loir: Jahresb. fur Chem. 1861,729. Tichanowitsch : Jahresb. 1864, 582. Grange: Jahresb. 1869, 752. Schiitzenberger : .Liebigs Ann. 160, 94 (1871). Krecke : Arch. Feet-land, vii. (1872). Vignon : Jahresb. 1874, 884. Bouchardat: Jahresb. 1875, 790, and Comptes Rend. 84, 34 (1877). Miintz and Aubin : Jahresb. 1876, 149; Ann. Chim. Phys. [5] 10, 553 (1877). 2 Miintz and Aubin: Ann. Chim. Phys. [5] 10, 553. 3 Bouchardat : Ann. Chim. Phys. [4] 27, 68, 145. 4 Vignon: Ann. Chim. Phys. [5] 2, 433. DEPENDENCE OF OPTICAL ACTIVITY UPON CHEMICAL CONSTITUTION. 35 has shown that nearly perfectly inactive mannite solutions become strongly dextro-rotatory oil the addition of borax. Again, ac- cording to Miintz and Aubin, 1 inactive glucose becomes strongly dextro-rotatory on the addition of sodium sulphate, and still more so of borax; addition of sodium carbonate produces, on the contrary, left-rotation. Moreover, the activity of organic acids and also of alkaloids is in most cases increased by their conversion into salts, and sometimes very considerably. The reverse also happens, as, for example, in the case of chloride of laudanine, which Hesse 2 reports as inactive, although the free base is Isevo-rotatory. Papaverine exhibits the same property. 4. In the preceding cases we have spoken only of the synthesis of bodies the chemical structure of which is identical with that of the natural substances, but where structural differences exist there will obviously be dissimilarity of optical power. Thus inactive paraconine from butyric-aldehyde is not an imide base like the active natural conine (Schiff 3 ), and accordingly differs from it in its other structural properties. 16. Optical Properties of Derivatives of Active Substances. It has long been observed that when optically- active substances undergo chemical changes, some of their derivatives exhibit rotatory powers whilst others do not. Where the molecular constitution remains unaltered, as in the conversion of acids into salts, ethers, amides, &c., or in the combination of alkaloids with acids, the activity is usually retained. 4 On the other hand, where there is actual chemical decomposition, active and inactive derivatives are obtained with an apparent absence of all rule. If, however, the hypothesis of asymmetrical carbon-atoms be called into aid, the apparent irregularity vanishes, and the conditions, as van't Hoff 5 has shown, resolve themselves into the following : 1. The rotatory powers of active substances are obliterated in such of their derivatives as are wanting in asymmetrical carbon- atoms. 1 Miintz and A.ubin: Ann. Chim. Phys. [5] 10, 564. 2 Hesse: Liebig's Ann. 176, 198, 201. 3 Schiff: Liebig's Ann. 157, 352 ; 166, 94. 4 Exceptions exist in laudanine and papaverine, which, as mentioned in 15, when free are optically -active, but in the form of chlorides are inactive (Hesse). 5 J. van't Hoff: see the two pamphlets mentioned in note 7, p. 24 of the present work; also Ber. d. deutsch. chem. Gesell. 1877, 1620. D 2 36 GENERAL ASPECTS OF OPTICAL ACTIVITY. As examples may be cited : 1 . From Active Tartaric and Malic Acids is derived Inactive Succinic Acid. (by treating with hydriodic acid or by fermentation) 2. ,, ,, Cane -sugar and Tartaric Acid ,, ,, Oxalic Acid. (by treating with nitric acid) ,, Tartaric Acid (with phos- ,, ,, Chloro-maleic Acid. phoric chloride) ,, Lgevo-malic Acid (by heating) ,, , 3. 4. 5. 6. 7. 8. 9. 10. Leevo-malate of Ammonia (by heating) Asparagin (by fermentation) Glucose (by fermentation) Carbo-hydrates (with sul- phuric acid) Amyl-alcohol Maleic Acid and Fu- maric Acid. Fumarimide. Succinic, Maleic, and Fumaric Acids. Ethyl-alcohol. Furfurol. Amyl hydride, Amy- lene,and Methyl-amyl. Bitter Almond Oil. ,, Amygdalin (by fermentation) ,, , In none of the above derivatives do anv asymmetrical C-atoms occur. See formulae on a previous page (p. 27 arid following pages). 2. Derivatives of active substances, when such derivatives con- tain asymmetrical carbon-atoms, usually exhibit rotatory power. As examples may be taken : 1. From Active Amyl-alcohol (by oxi- is derived Active Valerianic Acid, &c. dation) 7. 8. 9. 10. Camphor (with nitric acid) Amygdalin (by boiling with baryta- water) Amygdalin (with hydro- chloric acid) Asparagin (by boiling with acids or alkalies) Aspartic Acid (with nitrous acid) Dextro-tartaric Acid (with hydriodic acid) Cane-sugar, Mannite, Glu- cose, and Laevulose (with nitric acid) Saccharic Acid (with nitric acid) Milk-sugar (with nitric acid) Camphoric Acid. Amygdalic Acid. Mandelic Acid. Aspartic Acid. Dextro-malic Acid. Dextro- malic Acid. Saccharic Acid. Dextro-tartaric Acid. Dextro-tartaric Acid. On the other hand, cases occur in which such derivatives, the presence of asymmetrical carbon-atoms notwithstanding, exhibit DEPENDENCE OF OPTICAL ACTIVITY UPON CHEMICAL CONSTITUTION. 37 no rotatory power, as the subjoined (compare with the formulae previously given, page 27 and following pages) : 1 . From Active Malic Acid (with is derived Inactive Monobromo-succinic Acid. hydrobromic acid) 2. ,, ,, Dextro-tartaric Acid ,, ,, Pyro-tartaric Acid. (by heating) 3. ,, ,, Lactose (with nitric ,, ,, Mucic Acid. acid) A conversion of active substances into inactive isomers fre- quently results from exposure to a higher temperature. Dextro- tartaric acid, heated in presence of water to a temperature of 160 Cent., is converted chiefly into inactive, undecomposable tartaric acid ; whereas, at a temperature of 175 Cent., a mixture of the latter with a predominance of para-tartaric acid is obtained. Con- versely, at a temperature of 160 Cent, para-tartaric acid is converted into the other inactive tartaric acid (Jungfleisch). 1 Again, dextro- camphoric acid mixed with a little water, and raised to a temperature of 170 to 180 Cent., passes into inactive camphoric acid (Jung- fleisch 3 ) ; and active amyl-alcohol when heated in sealed tubes becomes inactive (Le Bel 3 ) . The conversion into the inactive state is often assisted by the presence of other substances. Thus fermentation- amyl-alcohol loses its rotatory power when distilled under ordinary pressure in presence of caustic potash, caustic soda, or chloride of calcium (Balbiano 4 ). By merely heating in a sealed tube for a quarter of an hour at 250 Cent, with a few drops of concentrated sulphuric acid, active valerianic acid is rendered inactive (Erlenmeyer and Hell 5 ). Repeated agitation with one-twentieth of its volume of concentrated sulphuric acid in the cold, and subsequent distillation, converts active turpentine-oil into inactive terebene (Riban 6 ). The case of tartaric acid indicates the probability that such conversions of active into inactive substances are due to the simultaneous formation of right-rotating and left-rotating modifications, resulting in optical neutrality. In turpentine- oil a gradual conversion of the right-rotating into the left-rotating form has been noticed. If the oil is placed 1 Jungfleisch: Ber. d. deutsch. chem. GeselL 1872, 985; 1873, 33. 2 Jungfleisch: Jahresb.fur Chem. 1873, 631. 3 Le Bel : Jahresb.fur Chem. 1876, 347. * Balbiano: Jahresb.fur Chem. 1876, 348. 5 Erlenmeyer and Hell : Liebig's Ann. 160, 302. 6 Riban: Jahresb. fur Chem. 1873, 370. 38 GENERAL ASPECTS OF OPTICAL ACTIVITY. in a retort provided with an upright condenser, and, whilst the retort is kept filled with carbonic acid at the ordinary pressure of the atmosphere, the contents are raised to boiling, whereby a temperature of 160 to 162 Cent, is attained, no change of rotatory power can be detected at the end of sixty hours. But such change occurs when the temperature passes beyond 250 Cent, in a sealed tube. A sample of English right-rotating turpentine-oil, which gave an original deviation of ctj = + 18*6 in a layer of 100 millimetres, showed the following angles of rotation at higher tem- peratures : After 4 hours at 250 Cent. a,. = + 15'3 After an additional 4 250 to 260 Cent. a,. = + 11'8 60 250 to 260 Cent. a,.'=- 8'6 42 about 300 Cent. a,. = - 5'6 At a certain stage an inactive mixture of right-rotating and left-rotating molecules must therefore have been present (Berthelot 1 ). Polymerization occurs simultaneously with the above changes. This can readily be produced without any change of temperature, by treating with antimony trichloride, whereby, for example, left-rotating terebenthene is converted into right- rota ting tetra- terebenthene (Riban 2 ). In certain cases, two isomeric derivatives possessing opposite rotatory powers but of unequal intensity are simultaneously formed from an active substance, the immediate product being therefore also active. By heating mannite to 150 Cent., or treating it with muriatic acid, we obtain a right-rotating mixture, which on evaporation separates out the crystallizable laevo-mannitan, leaving amorphous dextro-mannitan in the mother liquor (Bouchardat 3 ). Again, cane-sugar is transformed by the action of ferments or dilute acids into left-rotating invert-sugar, which can be split into right- rotating glucose (dextrose) and left-rotating glucose (laevulose). On the other hand, cane-sugar exposed with one-twentieth part water, in a sealed tube, for the space of two or three minutes, to a temperature of 160 Cent., gives an inactive glucose, which appears to be in- divisible (Mitscherlich, 4 Miintz and Aubin 5 ). 1 Berthelot: Ann. Chim. Phys. [3], 39, 10* 2 Riban: Bull Soc. Chim. [2], 22, 253. Jahresb.fiir Chem. 1874, 451. 3 Bouchardat: Jahresb.fiir Chem. 1875, 792. 4 Mitscherlich : Lehrbuch der Chem. 4 Aufl. I, 337. 5 Miintz and Aubin: Ann. Chim. Phys. [5], 10, 564. DEPENDENCE OF OPTICAL ACTIVITY UPON CHEMICAL CONSTITUTION. 39 The direction of rotation in derivatives, in relation to that in the parent substance, follows no fixed rule. Most derivatives exhibit their rotatory power in the same direction as the parent substance, particularly when no real alteration of molecular constitution has taken place. This is seen in the conversion of active acids and alkaloids into their salts. Still there are exceptions here, as we find that malic acid, which is left-rotating when free, is right-rotating in its neutral salts, especially in the double salt of antimony and ammonium, from which, after precipitation of the antimony with sulphuretted hydrogen, a left-rotating solution of acid malate of ammonia is obtained (Pasteur 1 ). Again, right-rotating para-lactic acid has left -rotating zinc and calcium salts (Wislicenus 2 ). But even in more profound reactions the original direction is generally main- tained. Thus, dextro-tartaric acid gives dextro-malic acid; from dextro-camphor we get dextro-camphoric acid ; from laevo-camphor, laevo-camphoric acid ; dextro- and laevo-borneols give respectively dextro- and laevo-camphors ; and left-rotating amygdalin gives left- rotating amygdalic and mandelic acids (Bouchardat 3 ). Neverthe- less, some derivatives do exhibit rotatory power in a direction contrary to that of the parent substance, as in the following instances : Dextro-camphoric acid gives left-rotating camphoric anhydride (Montgolfier 4 ) ; dextro-para-lactic acid gives left-rotating ether-anhy- drides (Wislicenus 2 ) ; the active compounds derived from laevo-arnyl- alcohol (amyl chloride, amyl iodide, amyl cyanide, diamyl, ethyl-amyl, amylamine, amyl valerate, valerianic aldehyde, valerianic acid, and capronic acid) are all right-rotating ; left-rotating santonic acid, with nascent hydrogen passes into right- rotating hydrosantonic acid (Cannizarro 5 ) ; left-rotating terebenthene hydrochlorate, heated with stearate of soda, gives left-rotating terecamphene. By saturating the latter with hydrochloric acid we get right-rotating camphene hydrochlorate, from which, by heating with water, left-rotating cam- phene, but with rotatory power much feebler than at first, can be recovered (Riban 6 ). Again, mannite, with weak laevo-rotatory power, gives both right- and left-rotating derivatives. Of these nitro-mannite, mannite hexacetate, amorphous mannitan, nitro- 1 Pasteur: Ann. Chim. Phys. [3] 31, 67. 2 Wislicenus: Liebig's Ann. 167, 322 3 Bouchardat: Comptes Rend. 19, 1174. 4 Montgolfier: Jahresb. fur Chem. 1872, 569. 5 Cannizarro: Jahresb. fur Chem. 1876, 619. 6 Biban : Bull. Soc. Chim. [2], 24, 10. 40 GENERAL ASPECTS OF OPTICAL ACTIVITY. mannitan, mannitan tetracetate, mannitan monochlorhydrin are right- rotating ; \vhilst mannite dichlorhydrin, crystallizable mannitan, and mannitone are left-rotating (Yignon, 1 Bouchardat 3 ). By oxidation of dextro-camphor with nitric acid we obtain, simultaneously with right- rotating camphoric and camphic acids, left-rotating camphoronic acid as well (Montgolfier 3 ). Lastly, the remarkable fact must be mentioned that in certain cases active substances exhibit changes in the direction of their rota- tory powers, when dissolved in various liquids or when certain substances are added to their solutions. Asparagin and aspartic acid are left-rotating in alkaline (i.e. sodic, or ammoniacal) solutions ; but in acid (i.e. hydrochloric or nitric acid) solutions, on the con- trary, they are right-rotating (Pasteur 4 ). The acid ammonium salt of Isevo-rotatory malic acid exhibits left-handed rotation in aqueous and ammoniacal solutions ; in nitric acid it forms a right-rotating solution (Pasteur 4 ). The calcium salt of dextro-tartaric acid is dextro- rotatory in aqueous and Isevo-rotatory in hydrochloric acid solution ; whilst, on the other hand, laevo-tartrate of lime is dextro-rotatory in hydrochloric acid solution (Pasteur 5 ). An aqueous solution of mannite, which, as such, manifests a very feeble left-handed rotation, becomes strongly laevo-rotatory, on addition to the solution of certain alkalies (as caustic potash, caustic soda, magnesia, lime, baryta), and dextro-rotatory, in presence of salts of the alkalies (as borax, chloride of sodium, sodium sulphate, potassium hydrarseniate) . Ammonia renders it feebly dextro-rotatory, but acids have no effect upon it (Yignon, 6 Bouchardat, 7 Miintz and Aubin 8 ). Similar properties are exhibited to a remarkable extent by ordinary tartaric acid. In aqueous solution it is dextro-rotatory, whilst in the solid state it may assume a Isevo-rotatory power ( 19). The rotatory power of its aqueous solutions is very considerably in- creased by the addition of even small quantities of boric acid, or borax ; on the other hand, it is diminished by the addition of sulphuric, hydrochloric, or citric acid, and also of alcohol or wood-spirit (Biot 9 ). 1 Vignon: Jahresb.fiir Chem. 1874, 885. 2 Bouchardat: Jahresb.fiir Chem. 1875, 790792. 3 Montgolfier : Jahresb.fiir Chem. 1872, 569. 4 Pasteur: Ann. Chim. Phys. [3], 31, 67. Jahresb.fiir Chem. 1851, 176. 5 Pasteur: Ann. Chim. Phys. [3], 28, 56. Jahresb.fiir Chem. 1849, 128. 6 Vignon : Ann. Chim. Phys. [5], 2, 433. Jahresb.fiir Chem. 1874, 884. 7 Bouchardat: Comptes Rend. 80, 120. Jahresb.fiir Chem. 1875,145. 8 Miintz and Aubin : Ann. Chim. Phys. [5], 10, 553. Jahresb.fiir Chem. 1876, 149. 9 Biot : Mem. de VAcad. 16, 229. DEPENDENCE OF OPTICAL ACTIVITY UPON CHEMICAL CONSTITUTION. 41 If, moreover, tartaric acid is dissolved in acetic ether or acetone, the resulting solutions, which either are inactive or may exhibit a feeble laevo-rotation, become immediately dextro-rotatory, on the addition of a little water. Malic acid appears to possess similar peculiarities. Phenomena of this sort differ from those exhibited by derivatives, in that the changes in the direction of rotation are temporary only, and disappear with the removal of the substances which induce them. The whole series of phenomena of this kind require, however, fuller investigation before the subject can be properly explained. III. PHYSICAL LAWS OP CIRCULAR POLARIZATION. 17. Amount of Rotation dependent on the Thickness of the Medium. From experiments with quartz, Biot, 1 in 1817, deduced the following laws : 1 . The angle, through which the plane of polarization of a ray of given wave-length rotates, is directly proportional to the thickness of the quartz plate. 2. Dextro-rotatory and Isevo-rotatory plates of quartz of equal thickness, cause the plane of polarization to deviate through equal angles. If the ray be transmitted through more plates than one, the final deviation is equal to the sum of the individual deviations if the plates all rotate in the same direction, and to their collective differences if they rotate in different directions. To allow comparison to be made of the rotatory powers of different active crystals, Biot proposed to adopt as a standard the angle of rotation afforded by plates 1 millimetre ('039 in.) in thickness. In active liquids (as, for example, oil of turpentine, or solutions of active solid substances in inactive liquids) the following laws have been observed : 1. The angle of rotation is directly proportional to the thick- ness of layer traversed by the ray. 2. When a ray is transmitted ^through several media, the observed rotation will be the algebraical sum of the individual rotations. As the rotatory power is generally much weaker in liquids 1 Biot: Mem. de I'Acad. 2, 41. PHYSICAL LAWS OF CIRCULAR POLARIZATION. 43 than in crystals, Biot proposed that the angle of rotation for thicknesses of 1 decimetre (3 '9 in.) should be taken as the standard of comparison for the former. 18. Amount of Rotation dependent on the Wave-length of Trans- mitted Ray. Rotatory Dispersion. If a series of polarized rays of different colours be transmitted successively through an active medium, it is found that the amount of rotation which the plane of polarization experiences, varies with the wave-length of the ray, being least for red, and greatest for violet. From his ex- periments with quartz, Biot arrived at the conclusion, that the angle of rotation a varies inversely almost exactty as the square of the wave-length of ray A, but this has not been confirmed by T> later observers. The formula a = A -f , in which A and B are A two constants, has also been found unsatisfactory ; whereas the equation since proposed by Boltzmann, 1 B C a '- * + F' which, like the preceding, contains two constants only (B and C), and which is based upon the assumption that rotation in a ray of infinite wave-length = 0, has been shown to agree very closely with the results of observation. For a complete determination of the rotatory power of a given substance, it is necessary to take the angles of rotation for a number of different rays of known wave-lengths. This can only be fully accomplished with the aid of Fraunhofer's lines ; that is, by the use of solar light, the deviations being determined by the method of Broch ( 61, 62, 63). Y. von Lang 2 has lately employed artificial light, the lithium, sodium, and thallium rays, for the same purpose. In the case of quartz, the angles of rotation for different lines have been accurately determined by Broch, 3 Stefan, 4 Soret and Sarasin, 5 and von Lang. 6 The table on page 44 contains the obser- vations of Stefan and von Lang, along with the corresponding wave-lengths A, expressed in millimetres. 1 Boltzmann: Pogg. Ann. -Jubelband, p. 128. 2 von Lang : Pogg. Ann. 156, 422. 3 Broch: Dove's Eepert. d. Phys., 7, 115. 4 Stefan : Sitzungsber. der Wiener Acad. 50. Pogg. 'Ann. 122, 631. 5 Soret and Sarasin : Pogg. Ann. 157, 447. 6 von Lang 1 : ut supra. 44 PHYSICAL LAWS OF CIRCULAR POLARIZATION. Ray. \. a for 1 millim. B 0-0006871 15-55 C 6560 17-22 D 5888 21-67 E 5269 27-46 F 4860 32-69 G 4309 42-37 H 3967 50-98 Li. 0-0006703 16-43 So. 5888 21-64 Th. 5346 25-59 From the foregoing measurements Boltzman has deduced the dispersion-formula 7-07018 0-14983 10 6 . X 2 10 12 . A 4 which does not differ from the results of actual observation by more than the hundredth part of a degree. For ray D different observers have obtained the following values :Biot, 20-98; Broch, 21'67 + 0-11; Stefan, 21-67; Wild, 1 21-67 ; von Lang, 21-64 at a temperature of 13-3 Cent.; Soret and Sarasin 21*80, at about 35 Cent. According to Scheibler 2 , quartz from different places, and even from the same place, is not quite constant in its rotatory power. As von Lang has shown, the rotatory power of quartz increases with rise of temperature, the relative alteration for different rays remaining the same. At we have Li. So. Th. a 16-402 21-597 26-533 and for any given temperature t, a t = o (1 + 0-000149 t). According to the later researches of Sohncke, 3 a t = a (1 + 0-0000999 t + 0*000000318 P) expresses the value more accurately. Extending the investigation to other substances, we find that not only do the absolute values of rotation in any one substance vary for different rays, but also in different substances the values vary by a different series of proportions that is, different bodies have different powers of rotatory dispersion. 1 "Wild: Veber ein neues Polaristrobometer. Berne, 1865, p. 55. 2 Scheibler: Zeitsch. des Vereinsfur Rubenzuckerindustrie. 1869, p. 388. 3 Sohncke: Wied. Ann. 3, 516. PHYSICAL LAWS OF CIRCULAR POLARIZATION. 45 For example, taking the following observations: 1 B C D E F G Quartz . a 1 millim. 16 50 17-22 21-67 27-46 32 69 42-37 Sugar . M 1 decim. + 47 56 52-70 66-41 84-56 101 18 131-96 Cholalic Acid w ,, + 28 2 30-1 33-9 44.7 52 7 67-7 Cholesterin n _ 20 63 25-54 31-59 39-91 48 65 62-37 Oil of Turpentine a _ 21 5 23.4 29-3 36-8 43 6 55-9 Oil of Lemon '; a + 34 37-9 48-5 63-3 77 5 106-0 B D E F G 1 1-11 1-39 1-77 2-10 2-72 1 1-11 1-40 1-78 2-13 2-77 1 1-07 1-20 1-59 1-87 2.40 1 1-24 1-53 1-93 2; 36 3-02 1 1-09 1-36 1-71 2-03 2-60 1 I'll 1-43 1-86 2-28 3-12 and calculating the ratios of rotation experienced by rays (7, D, E, F, .G, as compared with that by ray B, we get the following results : Quartz . . Sugar Cholalic Acid Cholesterin . Oil of Turpentine Oil of Lemon , It will be seen that the ratios in the case of sugar and quartz agree very closely. These two substances have thus equal powers of rotatory dispersion, while the others have either less or more than quartz. This fact has been turned to account in the construction of the Soleil (and Ventzke-Scheibler) saccharimeter, the principle of which supposes the rotatory dispersion of the active substance to be equal to that of quartz. But, so far as we know, this is only the case with cane-sugar, so that other substances cannot be properly examined with instruments of this description. In the majority of cases, the determination of the rotation for several rays would be too troublesome, and it is considered sufficient to determine it for a single ray. In Wild's polariscope, and in the so-called "half-shade" instruments of Jellett, Cornu, and Laurent, the light is supplied by a sodium flame, thus giving the angle of rotation for ray D of the solar spectrum. If a polariscope consisting simply of two Nicol prisms be used, it is requisite to employ monochromatic light (sodium flame) in order to get reliable results. With Soleil's saccharimeter, as well as those of Yentzke, Scheibler, and Hoppe-Seyler, which are all made on the same optical principle, white (gas-lamp) light is used, and the rotation given is for the so-called transition tint that is to say, the colour complementary 1 The values for oils of turpentine and lemon (given by Wiedemann, Pogg. Ann. 82, 222) are the angles of rotation a, directly determined with a layer 1 decimetre in depth; whilst those for cane-sugar (Stefan, Sitzungsber. der Wiener Acad., 52, 486, II te Abth.), anhydrous cholalic acid (Hoppe-Seyler, Journ. furprakt. Chem. 89, 257), and cholesterin (Lindenmeyer, Journ. fur prakt. Chem. 90, 323), express the specific rotation [a]. For cholesterin the solvent used was alcohol; for sugar and cholalic acid, water. 46 PHYSICAL LAWS OF CIRCULAR POLARIZATION. to mean yellow light the wave-length of which may be taken at about 0*00055 millimetre. The angle of rotation and the specific rotation thus obtained are indicated by a^ and [a]j (jaune moyeri) respectively, as proposed by Biot. Now the wave-length of this mean yellow light is less than that of the ray D, which lies on the border between orange and yellow, so that the value of cij is always less than that of a D l . For example, with quartz, according toBroch, a D = 21*67, and ctj = 24*5, so that, to express the one in terms of the other, we have 24*5 ttj = 21~*67 aj)= l'1306a D , or approximately = 9 / 8 a D ; 21*67 a D =" TTTF ^' = 0'8845aj, or approximately = 8 /9 a j- The proportion, however, between a, and a D varies in different substances, according to their different rotatory dispersions. J. de Montgolfier 2 has determined it in the following : Quartz (according to Broch) O D : a,- = 1 : 1-131 Aqueous solutions of Sugar ,, 1 : 1*129 Alcoholic solutions of Camphor ,, 1 : 1-198 Oil of Turpentine ,, '1 : 1-243 According to L. Weiss, 8 in aqueous solutions of sugar contain- ing 5 to 19 grammes in 100 cubic centimetres, the proportion is a D : Oj = 1 : 1*034. In any other substance, the rotation for one ray can be estimated from that for the other only approximately, by assuming that the rotatory dispersion of the substance agrees with that of some one of the preceding. As the transition tint corresponds to no sharply -defined ray, its use is attended with inconvenience, and latterly has been mostly abandoned. Many older observations are in existence, made by Biot with red light, obtained by transmission through glass coloured by suboxide of copper, with a refrangibility about equal to that of Fraunhofer's line C. Assuming that, on passing through a quartz plate 1 milli- metre thick, it experienced rotation through an angle of 18*414, "Wild 4 calculates its wave-length to be 0*000635 millimetre. The ratio between this red ray and the transition tint Biot 5 gives as 23 : 30. 1 By many observers the values of a, and a D have been taken as equal, a confusion which has been remarked upon by J. Montgolfier, Bull. Soc. Chim. 22, 487, and Riban, idem, 22, 492. 2 Montgolfier: Butt. Soc. Chim. 22, 489. 3 Weiss: Sitzungsber. der Wiener Acad. 69, 157, IH te Abth. 4 Wild : Polaristrobometer, p. 35. 5 Biot : Mem. de V Acad. 3, 177. PHYSICAL LAWS OF CIRCULAR POLARIZATION. 47 19. Abnormal Rotatory Dispersion. Although in ordinary cases the angle of rotation increases pari passu with the refrangibility of the ray, there are exceptions, as Biot, 1 and later Arndtsen, 2 have noticed in aqueous solutions of dextro-tartaric acid. This acid exhibits, in a remarkable degree, the property that its specific rotation [a] ( 24) increases with the diluteness of the solution from observation of which it is calculated. The increase is directly proportional to the dilution, and may be expressed by the formula [a] = A + B q, where q represents the percentage by weight of water in the tartaric acid solution. Arndtsen has determined by Broch's method the devia- tions for the Fraunhofer lines C, D, JE, b, F, e, in a series of solutions of different degrees of concentration, at a temperature of 24 Cent., from which he deduces the subjoined values for the constants A and B in the preceding formula : A [o] c = + 2-748 + 0-09446 q [o] D = + 1-950 + 0-13030 q [], = + 0-153 + 0-17514 q [] = - 0-832 + 0-19147 q [] = - 3-598 + 0-23977 q [a] e = - 9-657 + 0-31437 q Computing from these formulae the specific rotation for solutions containing from 10 to 90 percent, of tartaric acid, we get the annexed results : In 100 parts Solution Mo Red. E3. Yellow. Mi Green. Mu Green. OL Blue-green. []e Blue. Water f- Tartaric Acid. 90 10 11-25 13-68 15-92 16-40 17-98 (18-64) 80 70 20 30 10-30 9-36 12-37 11-07 14-16 12-41 14-49 12-57 (15-59) (13-19) 15-49 12-35 60 50 40 50 8-42 7-47 9-77 8-47 10-66 (8-91) 10-66 8-74 (10-79) 8-39 9-21 6-06 40 60 6-53 (7-16) (7-16) 6-83 5-99 2*92 30 70 5-58 (5-86) 5-41 4-91 3-60 - 0-23 20 80 (4-64) 4-56 3-66 3-00 1-20 -3-37 10 90 3-69 3-25 1-90 1-08 -1-20 -6-51 1 Biot : Mem. de V Acad., T5, 93. 2 Arndtsen: Ann. CMm. Phys. [3], 54, 403. Pogg. Ann. 105, 312. 48 PHYSICAL LAWS OF CIRCULAR POLARIZATION. From this table it appears that every solution exhibits a maximum of rotatory power for some one particular colour (as will be seen from the bracketed figures). In the most dilute solutions, containing 10 per cent, only of tartaric acid, the maximum is found, in its normal position, under the most refrangible ray e ; but as the concentration of the solution is increased it shifts towards the red end of the spectrum, and in the case of solutions containing 40 to 50 per cent, is found under the green rays. In 80 and 90 per cent, solu- tions the rotatory dispersion is entirely changed ; dextro- rotation is there at its maximum for the red rays, and decreases as the refrangibility of the rays increases, until under the blue ray it passes into laevo- rotation. Such is the case also with anhydrous tartaric acid. Now, according to the preceding formula of Arndtsen, this should be dextro- rotatory for the rays (7, D, E, laevo-rotatory for b, F, e, and inactive for light between E and I, and Biot l actually observed these pheno- mena in cast plates of tartaric acid ; moreover, Arndtsen 2 observed that the left-handed rotation for highly refrangible rays occurs when concentrated alcoholic solutions of this acid are used. The anomalies of rotatory dispersion in tartaric acid disappear when the solutions are exposed to higher temperatures (Krecke 3 ), or when mixed with a small quantity of boracic acid (Biot) ; moreover, they do not occur in the tartrates. Similar conditions may be produced artificially by mixing dextro- and laevo-rotatory solutions together in certain proportions. Biot 4 in this way obtained an achromatic compensation of the rotation for certain rays. Lastly, as regards the influence of temperature on rotatory dis- persion, Gernez 5 discovered that the application of heat, even to the extent of complete evaporation, produces no change in the dispersive powers of oils of turpentine, orange, bigaradia, and camphor. 1 Biot : Ann. Chim. Phys. [3], 28, 351. 2 Arndtsen: Ann. Chim. Phys. [3], 54, 415. 3 Krecke: Arch. Neerland, Bd. 7 (1872). 4 Biot : Ann. CKim. Phys. [3], 36, 405. 5 Gernez : Ann. de Vecole norm. 1,1. IV. SPECIFIC ROTATORY POWER. A. Definition of Specific Rotation. 20. In the discussions that follow certain abbreviations have been adopted viz. : a, the observed angle of rotation for a given ray. /, the length of liquid column used, in decimetres. d, the density of the rotatory liquid. p, the weight of active substance in 100 parts by weight of solution (per cent. composition) . C+q or by some other equation with several constants. In these formulae, A denotes the specific rotation of the pure substance. The values B (I.) and B and C (II.) represent the increase or decrease of A for 1 per cent, of inactive solvent. If q = 0, the specific rotation is that of the pure substance. On the other hand, if in equation I. or II., q = 100, we get for [a] a value which may be taken as the specific rotation of the active substance when infinitely diluted. Assuming that, when q = 100, the active substance vanishes and the solution consists of the inactive solvent alone, the rotatory power will then necessarily be nil. As Biot 2 has pointed out, this may likewise be deduced from the foregoing expres- sions by equating them with the formula [a] = > which is the specific rotation calculated from the directly observed angle of 1 The three constants A, B, and C of the formula [a] = A + - may, according L> -\- q to Biot (Ann. Chim. Phys. [3], 11, 96, 69), be calculated in the following manner: Given three separate solutions with q^ q z q z per cent, of active substance, and three specific rotation values [o^ [a] 2 [o] 3 respectively, then putting A + B = a, B C = b, C = c, the values a and c may be obtained from the equations : and then b may be found from any of the following equations Lastly, a--=A, - = B, c= C. C C Biot also brings the equation M-+^7 into the form, [] = A + 1 * q c , q , wherein ff * _* aild > d, specific gravity of the solution at 20 Cent., that of water at 4 being taken as unity. c = dp, the concentration, i.e., the number of grammes of active substance in 100 cubic centimetres of solution. I, the length of tube in millimetres, o, observed angle of deviation of rayZ), at a temperature of 20 Cent. , expressed in degrees and decimals (circular measure). [o] D = , the specific rotation for ray D, at a temperature of 20 Cent. L . c I. LEFT-HANDED OIL OF TURPENTINE. 30. Two kilogrammes of Bordeaux oil, after standing for several weeks over calcium chloride, were submitted to distillation. Nearly the whole came over between 160 and 162 Cent. Height of barometer = 737 millimetres. Specific gravity 0-86290. The rotation was observed with a Wild's instrument, having two bath-tubes of different lengths. Expt. L. I. 99-92 II. 21979 Mean: [o] D = 37'010. It should be remembered that when oil of turpentine is kept in vessels containing air, it undergoes a process of oxidation, whereby the specific gravity of the oil is increased and the rotatory power diminished. A portion of the above oil, after standing thus for four weeks, gave a specific gravity of '86779, and with a 219*79 millimetre tube showed a deviation of 68-144, whence [a] D = 35 '728. (a.) Mixtures with Alcohol. Alcohol, as nearly as possible anhydrous, with a specific gravity 07957, was used. The following mixtures were examined with Wild's polariscope : a. 31-905 70-204 37-004, 37-016. N , Oil of U S ^ ; ^P 611 - Mixture. tme Alcohol d. a for L = 219-79. MB- P- I. 90-0530 9-9470 ! 0-85558 77-0474 62-716 37-035 II. 69-9416 30-0584 0-83923 58-6971 48 052 37-247 III. 49-9658 50-0342 0-82542 41-2428 34-036 37-548 IV. 29-9715 70-0285 0-81273 24-3588 20-293 37-904 V. 10-0078 89-9922 0-80108 8-0170 6-782 38-486 DETERMINATION OF TRUE SPECIFIC ROTATION. 67 Like the oil itself its alcoholic solutions suffer a gradual decrease of rotatory power when kept in incompletely filled vessels. Mixture II. at the end of eight days gave [a] D = 37*164. (b.) Mixtures with Benzene. Crystallizable benzene with a boiling point 80*4 Cent, (baro- meter, 755 millimetres), and a specific gravity of 0*88029 was used. Observations were taken with Wild's instrument : Number Oil of i of Mixture. Turpen- tine P- Be~nzeire ? d. c. H. f OT L = 219-79. MD I. 89-9185 10-0815 0-86340 77-6356 63-466 37194 II. 77-9272 22-0728 0-86439 67-3595 55-500 37-487 III. 65-0553 34-9447 0-86562 56-3131 46-789 37-803 IV. 51-0499 48-9501 0-86769 44-2955 37-175 38-184 V. 36-8987 63-1013 0-87050 32-1204 27-196 38-523 VI. 22-0557 77-0443 0-87377 20-0580 17-207 39-031 VII. 9-9839 90-0161 0-87713 8-7572 7-593 39-449 (c.) Mixtures with Acetic Acid. The glacial acetic acid used was rectified by two fractional crys- tallizations, and had a specific gravity 1*0502 at 20 Cent, corre- sponding to 99*8 to 99*9 per cent, of acetic acid. Wild's polariscope was used: Number of Mixture. on of Turpen- tine P- Acetic Acid * d. c. a for L =. 219-79. MB, I. 90-1636 9-8364 0-87565 78-9520 64-462 37-148 II. 78-0658 21-9342 0-89166 69-6082 57-228 37-406 III. 64-8610 35-1390 0-91163 59-1293 49-235 37-885 IV. V. 50-9737 22-9616 49-0263 77-0384 0-93530 0-99183 47-6757 22-7740 40-266 19-858 38-427 39-672 VI. 9-8414 90-1586 1-02330 10-0707 8-903 40-222 F 2 68 SPECIFIC ROTATORY POWER. In these mixtures also an increase of density along with diminu- tion of rotatory power could be detected by keeping. After standing for three days, the following results were obtained : Mixture I. d = 0-87630 a = 63-987 [a] = 36-847 (when fresh 37" 148). ,, IV. rf = 0-93540 a = 39-859 [a] = 38-034 (when fresh 38-427). By reason of this liability to change under the influence of oxidation, oil of turpentine is not altogether a suitable substance for experiments of the above kind, and inattention to this point at the outset entailed the necessity of repeating several of our experiments. Fig. 15. As the observations show, the specific rotation of the oil of turpentine rises with the addition of increasing quantities q of all three solvents, the graphic representations taking the form of curves, of which that for acetic acid appears steepest, that for benzene less so, and for alcohol least (see Fig. 15). Although the curvature in each case is slight, the deviation from a straight line is too great to admit of application of the formula [a] = A + B q. If, taking this equation, we proceed to determine the constant A from two mixtures, values will be obtained, which will always be less DETERMINATION OF TRUE SPECIFIC ROTATION. 69 than the true specific rotation of pure oil of turpentine (37*01), differ- ing from the latter in proportion to the diluteness of the solutions employed in its determination. Thus, with alcohol as the inactive solvent, we get Divergence Extra- from 37*01 polation From mixtures I. and II. A = 36-93 0-80 10 percent. II. ,, III. A = 36-79 -0-22 30 III. IV. A = 36-66 -0-35 50 IV. V. A = 35-87 -1-14 70 On the other hand, if we adopt the formula [a] = A + B q + C q 2 , and compute the values of the constants A, B, and C from the solutions containing the smallest, mean, and largest proportions respectively of the inactive constituent, we get for A a value approaching very near to that of the specific rotation of pure oil of turpentine. Moreover, the formula agrees sufficiently well with the experimental curve throughout (from q = 10 to 90). The mixtures specified furnished the results shown below : 1. Alcohol (computed from solutions I., III., and V.) [o] D = 36-974 + 0*0048164? + 0*00013310 ? 2 . 2. Benzene (computed from solutions I., IV., and VII.) [a] D = 36*970 + 0*021531? + 0*000066727 ? 2 . 3. Acetic acid (computed from solutions I., IV., and VI.) [a] D = 36*894 + 0*024553? + 0*00013689 ? 3 . These formulse give the following interpolation values : Solvent Medium. No. of Mixture. s- MD Observed. Mb Calculated. Difference. Alcohol II. IV. 30-0584 70-0285 37-247 37-904 37-239 37-964 - 0-008 + 0-060 II. 22-0728 37-487 37-478 - 0-009 Benzene III. V. 34-9447 63-1013 37-803 38-523 37-804 38-594 + 0-001 + 0-071 VI. 77-0443 39-031 39-025 - 0-006 ( II. 21-9342 37-406 37-498 + 0-092 Acetic Acid < III. 35-1390 37-885 37*926 + 0-041 ( V. 77-0384 39-672 39-598 - 0-074 70 SPECIFIC ROTATORY POWER. If now we seek to determine the specific rotation of pure oil of turpentine from the more dilute solutions only, we get for A in the formula [a] = A + B q + C q* values showing the following divergences : From Solu- We obtain Divergence Extra- Solvent. tions A = : from 37-01 polation Alcohol ( II, IV, V. 37-20 + 0-19 30 percent. \ ILL, IV, V. 35-13 - 1-88 50 Benzene | IIL, v. VI. 37-26 + 0-25 35 ( V VI, VII. 35-42 - 1-59 63 Acetic Acid | IL, IV, VI. 36-65 - 0-36 22 i IV, v. VI. 36-00 - 1-01 49 Hence the divergence from the real value may amount, in some cases, to a whole degree, when the solutions contain more than 50 per cent, of solvent. II. EIGHT-HANDED OIL OF TURPENTINE. 31. The American oil here employed had a specific gravity of 0-91083. For determining the rotation of the pure oil and its mixtures Wild's and Mitscherlich's instruments were used, but at the time these observations were made the experimental tubes had not been furnished with water-baths. The temperature of the liquid was ascer- tained at the conclusion of the measurements by a thermometer inserted into the tube. a for Instrument. Temperature. L = 219-90millims. [o] D . Wild 21-2 28-354 14-156 Mitscherlich 21-0 28-315 14-137 Mean : [a] D = 14-147. Mixtures with Alcohol. The following mixtures were prepared : Number of Mixture. Oil of Turpentine p. Alcohol 9> d. c. I. 73-0927 26-9073 0-87648 64-0643 II. 47-5124 52-4876 0-84642 40-2154 III. 22-2443 77-7557 0-81864 18-2101 DETERMINATION OF TRUE SPECIFIC ROTATION. The angles of rotation obtained were : 71 Number of Mixture. Instrument. Tempera- ture. a for L = 219-90. [a]. J] Mean. I Wild Mitscherlich 22-5 22-0 20-416 20-426 14-492 14-499 14-496 -I Wild Mitscherlich 22-0 22-0 13-096 13-059 14-809 14-767 14-788 ,,j Wild Mitscherlich 24-0 21-5 6-021 6-068 15-036 15-153 15-095 Here also the specific rotation undergoes a slight increase with increasing dilution. The graphic representation (Fig. 16) shows that Fig. 16. the three points lie almost exactly in a straight line. Introducing mean value of [a] into the formula [a] = A + B q, we obtain 1. Calculated from mixtures I. and II. A = 14-189 B = + 0-011415 2. II. III. = 14-150 = + 0-012150 3. I. ,, III. = 14-179 = + 0-011780 The values here obtained for A agree very closely with the directly observed specific rotation of the oil, = 14'147. Taking the mean of the above values for A and B, respectively, [o] D = 14-173 + 0-11782 q, which, of course, corresponds closely with the observations. We have - 7^ SPECIFIC ROTATORY POWER. W M Mixture. Observed. Calculated. Difference. I. 14-496 14-490 - O'OOG II. 14-788 14-791 + 0*003 III. 15-095 15-089 - 0-006 A further series of experiments with benzene as solvent led to no result, as the oil of turpentine used in preparing the mixtures was not uniform, from not all having been kept an equal length of time exposed to oxidizing influences. III. NICOTINE (LJEVO-ROTATORY). 32. The pure substance here employed was prepared from 400 grammes commercial nicotine (supplied by H. Trommsdorff, of Erfurt) . To remove any small impurities of ether, alcohol, and water, the liquid was heated in a retort, whilst a stream of hydrogen passed over it, for eight hours, at a temperature of 150, which was finally raised to 180 Cent., whereby a total distillate of 15 cubic centimetres, consisting chiefly of alcohol, passed over. The residue was then distilled in a current of hydrogen, in successive portions of 200 grammes, from a small retort heated by a sand-bath. At 225 Cent, the nicotine, at first still retaining some water, began to pass over, but the thermometer immersed in the liquid quickly rose to 244 (corrected, 249 Cent.) when the boiling proper began. Raised into the vapour, the thermometer fell to 241 '5 to 242 (corrected, 246'6 to 246'8 Cent.), which temperature re- mained constant during the rest of the distillation. Height of baro- meter, 745 millimetres. The hydrogen was admitted in a very slow stream, and no decomposition of the substance resulted. Altogether 350 grammes of pure substance, in the form of a colourless liquid, faintly tinged with yellow, were obtained. It was sealed up in glass tubes. An analysis of this nicotine, the nitrogen being determined in the gaseous form, gave the following numbers : Required for -^ , r< TT w .tound. G 10 1 14 JM 3 . C 74-02 73-95 H 8-66 8-92 N 17-32 17-55 The preparation was submitted to further examination by titra- tion. The nicotine was weighed in thin glass bulbs, which were then broken under water, and, after solution, tincture of litmus added, DETERMINATION OF TRUE SPECIFIC ROTATION. 73 and the liquid neutralized with a standard hydrochloric acid (con- taining 0-055013 gramme HC1 in 1 cubic centimetre). Analysis. Weighed Substance. Acid used in Titration. Hence 1 molecule H Cl (= 36-37) neutralized. I. II. III. 4-1303 grm. 1-0002 ,, 7-3048 ,, 16-9 c.c. = 0-92972 grm. H Cl 4-1 =0-22555 29-7 =1-63390 161-57 grm. substance 161-28 162-60 Mean 161-82 grm. of substance But one molecule nicotine, C 10 H 14 N 3 = 161 '72. Again, in a rough titration with dilute sulphuric acid, contain- ing 0*030369 gramme H 2 S0 4 per cubic centimetre, 37*1 cubic centimetres served to neutralize 3*8310 grammes of substance, accord- ing to which one molecule H 2 S0 4 (97*82) combines with 332'6 parts of nicotine ; but two molecules C 10 H 14 N 2 = 323*4. The specific rotation of the nicotine was observed with the Wild's instrument, and observations were taken at three separate tempera- tures (10, 20, 30 Cent.), so as to ascertain the effect of heat. The experimental tube was provided with a water-jacket, and, measured at the mean temperature (20 Cent.), had a length of 99*923 millimetres, from which its true lengths at 10 and 30 Cent, were calculated, assuming the coefficient of expansion of the glass to be 0*0000086. The specific gravity of the nicotine, referred to that of water at 4 Cent., was also observed with the pycnometer at each separate temperature. Temp. d. L. * a. Mo- 10-2 1-01837 99-914 millims. 163-776 160-96' 20-0 1-01101 99-923 ,, 163-204 161-55' 30-0 1-00373 99-932 162-450 161-96' Another analysis, made with Mitscherlich's instrument, using a ttfbe 49*82 millimetres long, gave a= 81*283. The temperature of the nicotine was about 21*0, and taking d = 1*01101, [a] = 161*38. Accordingly the specific rotation of nicotine at 20 Cent, has been taken in what follows as [a] D = 161*55. 74 SPECIFIC ROTATORY POWER. (a.) Mixtures with Alcohol. The alcohol used had a specific gravity of 07957 at 20 Cent. The following mixtures were observed with the Wild's instrument : Number of Mixture. Nicotine P- Alcohol 9- d. c. a for L = 99-923. [] I. 90-0945 9-9055 0-98839 89-0488 141-163 158-65 II. 74-9336 25-0664 0-95358 71-4553 110-616 154-92 III. 59-9345 40-0655 0-92001 55-1405 83-626 151-78 IV. 45-0846 54-9154 0-88747 40-0113 59-494 148-81 V. 30-0268 69-9732 0-85536 25-6836 37-319 145-42 VI. 14-9567 . 85-0433 0-82506 12-3401 17-460 141-60 To ascertain whether the solutions were affected by keeping, mixtures I. and Y. were left for a couple of days, and then examined again. The results gave for I. [a] = 158'63, and for V. [a] = 145 '45, which values agree almost perfectly with those above obtained from freshly-prepared solutions. As the table shows, the specific rotation of nicotine undergoes a pretty considerable decrease for successive additions of alcohol. Repre- sented graphically, it takes the form of a straight line, with but small divergences either way, and consequently the values of the constants in 'the formula [a] = A Bq do not materially differ, whichever of the solutions we take. Divergence from 161-55 C - 0-65 - 1-49 - 1-24 + 6-41 - 0-65 Here even dilute solutions yield values for A, which, considering the large rotation-angle of nicotine, come pretty close to the real value. Taking for A and B the mean of the above values, we get [o] D = 160-83 - 0-22236?, which gives the following interpolation values : From Mixtures We obtain A. I. and III. 160-90 II. IV. 160-06 III. V. 160-31 IV. VI. 161;96 I. VI. 160*90 Extra- polation = 10 per cent. - 0-22805 25 - 0-20490 40 - 0-21272 55 ,, - 0-23928 10 - 0-22686 DETERMINATION OF TRUE SPECIFIC ROTATION. 75 Number of Mixture. I. II. III. 53-12 52-28 51-41 + 0-01 o-oo o-oo Mono- / chlor- ) acetic t Ether I I. and II. II. III. I. III. 55-65 55-77 55-69 0-06608 0-06769 0-06677 f[a] D = 55-70 - 0-06685 0J I. II. III. 52-64 51-12 49-97 + 0-01 o-oo + 0-01 Benzene I. and II. II. III. I. III. 55-45 54-96 55-21 0-1683 0-1587 0-1620 ;[]== 55-21 -0-1630 q\ I. II. III. 49-19 47-00 42-87 -0-05 + 0-03 -0-08 Dimethyl-j aniline "j I. and II. II. III. I. III. 55-68 55-92 55-76 0-1472 0-1510 0-1491 x [ ] D =55-78-0-1491 q{ I. II. III. 49-40 46-25 43-13 + 0-03 -0-01 + 0-03 Wood- spirit I. II. III. [a] D = 56-15-0-1749 + 0-00066l7? 2 Alcohol I. III. V. 1 [a] D = 54-38-0-1614? + 0-0003690? 2(1 j II. IV. 47-21 43-33 + 0-28 -0-33 formula [a] = A + Bq + C q* must be taken as the basis of calcula- tion. The table annexed shows (1) the values of constants A and B, The formula [.] .'./* - gives [.]. = 54-83 - 8 SPECIFIC ROTATORY POWER. calculated from the several solutions ; (2) the derived interpolation- formulae obtained by putting in the mean values ; (3) the specific rota- tion of the solutions employed calculated from these equations, and the differences between these and the observed values, as given in the preceding table (p. 85). Comparing now with each other the values for constant A derived from different solvents, we find an agreement which, in view of the large amount of extrapolation from q = onwards, varying from 35 to 50 per cent., must be regarded as very close, and the mean of their values may accordingly be taken as the true specific rotation of pure camphor. The values for constant B, on the contrary, exhibit very marked variations. Calculating the specific rotation from the same formulae, by putting in limiting values q = and q = 1 00, we obtain the following as the range of variation which the rotatory power of camphor may undergo under the influence of various inactive liquids employed as solvents. Solvent. [a] D for^ = Pure Substance. [o] D for q 100 Infinite Dilution. Total Variation. Acetic Acid 55-5 41-8 13-7 Acetic Ether 55-2 50-8 4-4 Monochlor-acetic Ether 55-7 49-0 6-7 Benzene 55-2 38-9 16-3 Dimethyl - aniline 55-8 40-9 14-9 Wood-spirit 56-2 45-3 10-9 Alcohol 54-4 41-9 12-5 Lastly, taking the mean of the values obtained for the pure sub- stance, we have as the true specific rotation A^ of camphor, at a temperature of 20 Cent., A D = 55-4, with a mean variation of + 0'4. 37. In the same way the true rotation-constant of cane-sugar was determined by Tollens, 1 and simultaneously by Schmitz, 3 water being the only solvent used. In the case of sugar, the specific rotation 1 Tollens : Ber. d. deutsch. chem. Gesell 1877, 1403. 2 Schmitz: Idem., 1877, 1414; also, Zeltsch. d. Ver. fur Eiibenzuckerind. 1878, 48. DETERMINATION OF TRUE SPECIFIC increases with dilution, or, conversely, decreases with increase of con- centration, but the variations are small. Tollens examined seventeen solutions, of which the most concentrated, with 69 '2 144 per cent, by weight of sugar, gave a specific rotation [a] D = 65*490, and the most dilute with 3'8202 per cent., gave [a] D = 66'803. From the experi- mental results were derived the following interpolation -formulae for the calculation of the specific rotation of any given solution, by putting in values for p, percentage of sugar, and q t percentage of water respectively: (a) For strong Solutions, containing from 18 to 69 per cent, of Sugar. I. [a] D = 66-386 + 0-015035^ - 0-0003986 j? 8 . II. [a] D = 63-904 + 0-064686 q - 0-0003986 I. 64-9775 35-0225 1-31650 85-5432 56-134 65-620 II. 54-9643 45-0357 1-25732 69-1076 45-533 65-919 III. 39-9777 60-0223 1-17664 47-0392 31-174 66-272 IV. 25-0019 74-9981 1-10367 27-5938 18-335 66-441 V. 16-9926 83-0074 1-06777 18-1442 12-064 66-488 VI. 9-9997 90-0003 1-03820 10-3817 6-912 66-574 VII. 4-9975 95-0025 1-01787 5-0868 3-388 66-609 VIII. 1-9986 98-0014 1-00607 2-0107 1-343 66-802 The equation with reference to q, derived from these obser- vations, stands [a] D - 64-156 + 0-051596 q - 0*00028052 f ; according to which, the rotation-constant for pure sugar at a tempera- ture of 20 Cent, is A D = 64-16, 90 SPECIFIC ROTATORY POWER. which only differs from that obtained by Tollens by G'26 . 1 Tollens 2 has attempted, as Biot 3 had already done, to determine the rotatory power of anhydrous sugar directly, by employing plates cast from the melted substance. In this way he obtained a value considerably below that of the calculated specific rotation, viz., [a] D = 46*9. This is not surprising, as under the influence of heat sugar undergoes various important changes, as indicated by the assumption of a yellow coloration, as well as a strong reducing action on cupric salts. Even after solution in water, such a sugar exhibits a notably smaller rotatory power than before fusion, and the decrease is greater in proportion to the length of time during which it was kept fused (Hesse 4 ). Probably, in such cases a formation of inactive glucose takes place. 38. The true specific rotation of right-handed glucose (grape- sugar) has been determined by Tollens 5 both for the hydrate C 6 H 13 6 + H 2 0, and the anhydrous substance. In the subjoined table are given the solutions employed (with p per cent, by weight of glucose), along with the values of [a] D observed in each case, and side by side the values calculated from the interpolation-formulae given below. No. Hydrate of Glucose C 6 H 12 6 + H 2 0. Anhydrous Glucose C 6 H 12 6 . of Solution. p. [3 Observed at 20 C. [] Calculated. P> MD Observed at 20 C. MD Calculated. I. 8-4501 48-50 48-08 7-6819 53-35 52-89 II. 10-2216 48-18 48-12 9-2924 53-00 52-94 III. 10-3083 47-99 48-13 9-3712 52-79 52-94 IV. 11-0675 48-20 48-14 10-0614 53-02 52-96 V. 11-6907 48-16 48-16 10-6279 52-97 52-98 VI. 14-2459 48-34 48-23 12-9508 53-17 53-05 VII. 20-4832 48-55 48-41 18-6211 53-40 53-25 VIII. 34-7753 48-76 48-94 31-6139 53-64 53-83 IX. 44-8175 49-41 49-40 40-7432 54-35 54-34 X. 48-3870 49-70 49-59 43-9883 54-67 54-54 XI. 53-7534 49-66 49-88 48-8667 54-62 54-87 XII. 58-3254 50-15 50-15 53-0231 55-16 55-17 XIII. 90-8722 52-45 52-54 82-6111 57-70 57-80 1 This trifling difference is partly explained by Tollens having taken the specific gravity of the sugar solutions at a temperature of 17*5 Cent., whilst Schmitz took it at 20 Cent. The angles of rotation were observed by both at a temperature of 20 Cent. 2 Tollens : Her. der deutsch. chem. Oesett. 1877, 1413. 3 Biot : Mem. de I'Acad. 13, 130. 4 Hesse: Liebig's Ann. 192, 167. 5 Tollens : Ber. der deutsch. chem. Oesett. 1876, 1531. DETERMINATION OF TRUE SPECIFIC ROTATION. 91 (As the molecular weights of C 6 H 13 O 6 + H 2 and C 6 H 13 6 , and, therefore, also the corresponding values of p for the two substances, are in the ratio 198 : 180, or 11 : 10, the specific rotation of the hydrate and the anhydride must stand to each other in the inverse ratio 10 : 11.) As will be seen, the specific rotation increases with increase of concentration, or, conversely, decreases with increased dilution. Glu- cose thus exhibits a behaviour the reverse of that of cane-sugar. For glucose hydrate, the experiments gave the formula [ a ] D = 47-925 + 0-015534 1? + 0-0003883 jo 2 ; or, with reference to q, the percentage of water present in the solution : [o] D = 53-362 - 0-093194 q + 0*0003883 ? 2 . For anhydrous glucose, by raising the preceding values by one- tenth, we get the equations [o] D = 52-718 + 0-017087^ + 0*0004271 p\ [ a ] D = 58-698 - 0-10251 q + 0*0004271 (?. Lastly, from the foregoing formulae we get, as the true values of the rotation-constants, for C 6 H 12 6 + H 2 A = 53-36, n C 6 H 13 6 A D = 58-70. 39. Camphor, cane-sugar, and glucose 1 are the only solids, up to the present time, the direct specific rotations of which have been accurately determined. Numerous investigations, indeed, have been published as to the variation of the specific rotation in a large number of substances, but the observers have, as a rule, employed only solutions containing small percentages of active substance, so that only a few points have been determined, and that at the outer end of the respective curves, where the variation of rotatory power is at its maximum. From results of this kind the value for A cannot be determined. But, indeed, this were impossible at any rate, from the fact that neither the percentage composition by weight nor the density of the solutions is stated, but merely their concentration, i.e., the number of grammes of substance in 100 cubic centimetres. For the determination of individual values of [a] this is enough; but, as before explained ( 25), it is altogether insufficient for deter- mining the value of A. Nevertheless, in chemical writings we still find many specific 1 Arndtsen (see 19) has determined for tartaric acid the relation between specific rotation and percentage of water, and hence deduced the formula [o] D = 1 '95 + '1303 q, which gives the value for the pure substance A-Q = 1 '95. However, as the number of solutions observed was but small, a verification of the constants given is desirable. 92 SPECIFIC ROTATORY POWER. rotation-data based on the old view that the value is constant, and may be obtained by observation of a single solution of any optically -active substance. Accordingly, neither the weight-per- centage of active substance nor the concentration is stated, and in most cases no reference is made to the ray with which the observa- tions were made. For example, in many text-books the specific rotation of tartaric acid is given briefly thus : [a] = -f 9*6 ; whereas, as we have seen from the table already given ( 19), the specific rotation in solutions containing 10 to 90 per cent, of this sub- stance varies for the yellow ray D from 3*25 to 13' 68 ; for the green ray ~b, from 1'08 to 16'40 ; and for the blue ray e, as much as from 6 '51 to + 18 '64. Again, we find the specific rotation of cane-sugar given as [a] = + 73 to 74, without mention of the fact that this is the value for the transition tint, although for the neigh- bouring yellow ray D the value for solutions holding, say 25 per cent, of sugar, is, as shown in 37, only [a] D = 66'44, and the value ranges, moreover, for the same ray from 64 to 67, according to the degree of concentration of the solutions employed. That data of this sort, as remarked in 23, are utterly worthless, must now be obvious after what has been said. 40. The Specific Rotation exhibited by an Active Substance in a Solution of given Composition is Constant, and hence can be employed as a Distinguishing Characteristic of the Substance. But that it may possess this value, it is indispensably necessary that, along with the value of [a], the following data should be stated : 1. The ray with which the observations have been made the index- letter being placed after the bracket. 2. The description of solvent used (as water, alcohol, &c. ; in the case of the latter, either the per cent, composition or specific gravity being stated). 3. The proportion of active substance in 100 parts by weight of solution (per cent, composition^?), or else the number of grammes in 100 cubic centimetres of solution (the concentration c). 4. The temperature t, of the solution when the angle of rotation was observed. The determination of the specific gravity of the solution, or the adjustment of the volume in a graduated measure, must be done at this same temperature. 5. The direction of rotation (dextro-rotatory -f, laevo-rota- tory -). DETERMINATION OF TRUE SPECIFIC ROTATION. 93 These data may be recorded as follows : Cane-sugar (solution in water, p = 16*993, t = 20), [a] D = + 66-49. Ordinary camphor (solution in alcohol of specific gravity 0'796, at 20, p = 15-092, t = 20), [o] D = + 43-66. Santonin (solution in alcohol of 97 per cent, by volume, c = 2, t = 15), [o] D = - 174-00. Quinine hydrate, C 20 H 24 N 2 2 + 3 H 2 (solution in alcohol of 80 per cent, by volume, c. = 1, t = 15), [o] D = - 158-63. ,, (solution in alcohol of 80 per cent, by volume, c = 6,t = 15), [a] D = -- 114-92. (solution in a mixture of 2 volumes chloro- form + 1 volume alcohol of 97 per cent, by volume, c = 5, t = 15), [a] D = - 140'50. In this way Hesse 1 has estimated the specific rotation of a great number of optically-active substances dissolved in different liquids, thus supplying data which, as constant marks of the several substances, are of great value in determining the identity or purity of different preparations. In all cases it is advisable to record the per cent, composition p, rather than the concentration c of the solutions, and so to calculate the specific rotation bv the formula [a] = - - , which, moreover, '. d .p renders it necessary to determine the specific gravity of the solutions. The resulting values, at least in cases where several solutions have been observed, can then be used in determining the specific rotation of the absolute substance. This, as frequently already mentioned, is not the case when only the concentration is determined by means of a graduated vessel, and the specific rotation calculated by the otherwise . . - - a . 100 more convenient formula [a] - . / . c 41. Molecular Rotation. Specific rotation [a] is frequently referred to by Biot under the name of molecular rotation, indicating, as observed ( 10), that the rotatory power of liquids is a property resident in the molecules. 1 Hesse: Liebig's Ann.176,89, 189; 178, 260; 182, 128. Hesse indicates the number of grammes of active substance in 100 cubic centimetres solution by p. It is, however, much better to employ c for this purpose (concentration) and let p denote the true per cent, composition (or number of parts by weight of active substance in 100 parts by weight of solution). 94 SPECIFIC ROTATORY POWER. But this expression has been applied by Wilhelmy, 1 Hoppe- Seyler, 2 and more recently by Krecke, 3 to a different value, viz., to the number obtained by multiplying the specific rotation of any sub- stance into its molecular weight P. The values thus obtained being inconveniently large, Krecke has proposed to divide them uni- formly by 100. The' molecular rotation \_M~\ of a given substance then appears as which expresses the angles of rotation produced by passage of the ray through layers 1 millimetre thick of substances when the unit- volumes contain the same number of molecules. It has been attempted, by means of this formula, to discover relations between an active substance and its derivatives in respect to rotatory power, and the existence of certain multiple relations has been supposed to have been detected (Krecke, 3 Landolt 4 ). But the observations on which these comparisons were based were made, as was formerly the practice, with a single solution of each substance, whereas we have seen ( 34) that the constant A of the pure sub- stance should alone have been employed. Before, therefore, the hypothetical so-called law of multiple rotation is ripe for discussion a much more extensive series of experiments is necessary. 1 Wilhelmy : Pogg. Ann. 81, 527. 2 Hoppe-Seyler : Journ. fur prakt. Chem. [1], 89, 273. 3 Krecke: Journ. fur prakt. Chem. [2] 5, 6. 4 Landolt : Ber. der deutsch. chem. Gesell. 1873, 1073. Y. PROCESS OF DETERMINING SPECIFIC ROTATION. 42. In calculating specific rotations by the formulae given in 20, 21, viz., I. (For liquids) [a] = 1^0 -^, L . a II. (For solutions) [aj = L.p. a 10 4 . a the following data must be obtained by direct experiment : 1. The measurement of the angle of rotation a for a given ray. 2. The measurement of the length of the experimental-tube, in millimetres. 3. The weight p of active substance in 100 parts by weight of solution. 4. The specific gravity d of the active liquid. 5. The concentration c i.e., the number of grammes of active substance in 100 cubic centimetres of solution. If the object of determining the specific rotation of a solu- tion of a solid substance, is merely to obtain a characteristic of its presence in solution, formula III., based on the knowledge of its concentration c, will suffice. But if, on the contrary, it is desired to ascertain the actual specific rotation of the substance itself, from observations on a number of different solutions, it is neces- sary (see 25) to employ formula II., involving a knowledge of the percentage composition, and specific gravity of the several solutions. 96 PROCESS OF DETERMINING SPECIFIC ROTATION. A. Determination of the Angle of Rotation. POLARISCOPIC APPARATUS. 43. Apparatus for the Qualitative Examination of Rotatory Power. To determine merely whether a given substance is or is not optically-active, and, if active, the direction in which the Fig. 20. rotation takes place, the instrument here represented (Fig. 20 1 ), which is delicate enough to detect even feeble degrees of rotatory power, may be used. 2 A brass trough a b, of semi-circular section, fitted with a cover c so as to form a tube, carries at the extremity a, in a fixed case, a polarizing Nicol d. In front of the latter is placed the convex lens e, and on the other side of the polarizer at /, a so-called Soleil double-plate, formed of two plates, one of dextro-rotatory, the other of laevo-rotatory quartz, fitted vertically together and ground to a uniform thickness of either 375 or 7 '5 millimetres. The opposite end of the brass tube holds the movable Nicol g t 1 [/ is given apparently out of proper section, representing a front view, whilst the rest of the figure shows a longitudinal section. D.C.R.] 3 The instrument shown above is manufactured by F. Schmidt and Haensch, Stallschreiberstrasse 4, Berlin. Instruments on the same optical principle, but of simpler construction (described by C. Neubauer inFresenius' Zeitschr. fur analyt. Chem, 16, 213) intended for determining grape-sugar in wine, but equally applicable for all other active substances, are procurable from the Optical Instrument Works of Dr. Steeg and Reuter, Homburg v. d. Hche. DETERMINATION OF THE ANGLE OF ROTATION. 97 besides a small Gralilean telescope, consisting of an object glass h, and an ocular i. The Nicol is turned by the handle k, which moves round the face of a small graduated disc /, so as to allow the amount of rotation to be determined, at least approximately. The brass trough receives the glass tube p p (the ends of which may be closed by glass plates fixed with brass screw-caps) containing the liquid to be examined. The whole rests on a stand o. As a consider- able depth of liquid is requisite for the detection of feeble rotatory power, the brass case is so constructed as to take glass tubes 5 or 6 decimetres in length. It is to this, and the introduction of the Soleil double-plate, that the sensitiveness of this instrument is due. In using the instrument, the glass tube is at first left out whilst the extremity is directed towards a bright flame, for which pur- pose the gas-lamp, shown in Fig. 25, will be found best. The eye- piece of the telescope is then adjusted so that the vertical division of the double-plate appears sharply defined. By turning the analyzer <7, a certain position will readily be found in which the two halves of the field of vision exhibit a perfectly uniform purplish tint, which the least turn of the Nicol to the right or left changes, one half becoming red, the other blue. Further particulars of this so-called sensitive tint will be given later on ( 78) in speaking of the Soleil saccharimeter. Having thus established perfect uniformity of colour in the two halves of the field of vibion, with the index standing at the zero-point on the scale of the analyzer, the glass tube containing the liquid to be tested is laid in the trough, when its optical activity will at once be declared by inequality of tint in the field of vision. To know whether the rotation be right-handed or left-handed, it is requisite, in the first place, to determine in the instrument, once for all, what relative positions the red and blue take up when some substance of known rotatory power, such as a (dextro-rotatory) solution of cane- sugar, is inserted. If the substance under examination shows the colours in the same relative order in which they are shown by the sugar, it likewise is dextro-rotatory ; if the positions are interchanged, it must be laevo-rotatory. Further, with dextro-rotatory substances uniformity of tint in both halves of the field of vision is restored by turning the analyzer to the right, or in the direction of the hands of a watch, and with IODVO- rotatory substances, to the left. The position of the index on the graduated disc of the analyzer shows the angle of rotation in each case. H 98 PROCESS OF DETERMINING SPECIFIC ROTATION. Instead of this instrument any of the forms of polariscope described further on may be used. The advantage of the above instrument lies in its sensitiveness and the facility with which with it the direction of the rotation can be determined. 44. For the accurate measurement of the angle of rotation, a variety of instruments have been devised, which may be divided into two classes, according to their objects : 1. The so-called polaristrobometers, what in England are known as polariscopes, 1 which indicate the amount of rotation in angular measure, and are applicable to all optically-active sub- stances. 2. The saccharimeters, which are specially intended for the analysis of solutions of cane-sugar, the angular measurement being replaced in them by an empirical scale. (a.) MitscherUch' s Instrument* 45. This simplest of all forms of polariscope consists, as already stated ( 5), of a pair of Nicol prisms, placed one at each end of a brass or wooden rod or bar d, Fig. 21. The polarizer a is provided with a brass case, by means of which it can be turned if required, and then clamped with the small screw e. The circular movement of the analyzer b is effected with the handle c, the angle through which it is revolved being read off on a fixed graduated disc by means of opposite index arms, with or without verniers. The 1 [At this point something requires to be said as to the nomenclature of various polarizing- instruments. The word polariscope, commonly used in English for any instrument the essential parts of which consist of a polarizer and analyzer, and which may or may not be applicable for showing the rotation phenomena with which this work deals, has no such range of meaning in German, as will be seen by reference to the use of the word in describing a special contrivance, the Savart polariscope forming- part of the instrument described in 49. On the other hand, we have in English no word limited to describe what the Germans call rather clumsily a polaristrobometer, and the French a polar imetre, a polariscope that is of special form, suited to observe and to measure the rotatory power of substances. If we deemed it advisable to introduce an expression for the purpose, it seems that " rotation polarimeter " would, as nearly as possible, represent the German polaristrobometer ; but since the word polariscope has become so familiar to practical people it seemed better to retain it and make the- needed explanation. D.C.R.] 2 Mitacherlich : Lehrbnch der Cliem. 4 Aufl. Bd. 3, 36 1 (1844). DETERMINATION OF THE ANGLE OF ROTATION. 99 graduation is in degrees, and the reading is taken in degrees and tenths. The experimental tube / is laid between the prisms, and usually has a length of 2 decimetres (7'6 in.). For increasing the illuminating power and giving a circular field of vision, a small convex lens is inserted in the case of the polarizer. Fig. 21. Fig. 25 46. In using Mitscherlich's instrument, it will be found best to employ homogeneous yellow sodium light, thus determining the angle of rotation for ray D. To obtain a sodium flame which shall last for some time, the lamp, 1 shown in Fig. 22, may be used, which consists of a vertically adjustable Bunsen burner , with a sheet-metal chimney, having a side aperture, b. In the movable pillar d is inserted horizontally a small cross-bar, carrying at its extremity a bundle of fine platinum wires, arranged so as to form a small pointed spoon c, the hollow being filled with well-dried common salt ; the Laurent : Dingier' c Folyt. Joiirti. 223, 608. This lamp maybe obtained of Schmidt andHaensch, Berlin. H 2 100 PROCESS OF DETERMINING SPECIFIC ROTATION. spoon is moved forward to the front edge of the flame, and the salt fusing and running to the point, volatilizes, and produces an intense yellow colour. Or the stem d may be provided with a small brass revolving collar, having several arms with holes, into which can be fitted platinum wires with beads of salt fused on. When one bead is consumed the next arm is brought round to the flame, and so on. Instead of common salt calcined soda may be used, but this, whilst volatilizing more slowly, has less illuminating power. In making observations, the instrument should be set up at a distance of an inch or so from the flame, and a black screen placed behind the latter, so as to shut off extraneous light. The room should be darkened too, at least partially, as the observations in general are more satisfactory the darker the place is. The zero- point must first be determined. For this purpose the tube is put in its place either empty or filled with water, and the analyzer Fig. 23. set to the position of greatest darkness. If the circular field of vision is at all large, there will not be perfect obscuration over the whole, but merely a vertical dark band, getting lighter towards the sides, as in Fig. 23, and this band must be brought, by backward and for- ward motions of the analyzer, as nearly as possible into the middle of the field. Repeating the adjustment several times, and taking the mean of the readings on the disc, we get the true zero-point of the instrument. To make the zero of the scale agree, at least approximately, therewith, we set the index against the mark, loosen the clamp e (Fig. 21), and rotate the polarizer until the dark band appears in the middle. "Usually this correction is made by the instrument-maker himself. As before stated ( 4 and 5), there are two positions, 180 apart, at which the analyzing prism gives maxi- mum darkness, and the zero-point of the second, which must lie somewhere about 180 on the scale, should similarly be accurately determined by a few observations. If the tube, filled with active liquid, be now laid in the instru- ment, the analyzer having been previously set to zero, the field of vision will again appear bright, and in order to restore the black band it will be necessary to rotate the analyzer to the right in the case of a dextro-rotatory substance that is, in the direction of the hands of a watch and in the opposite direction, to the left, when the substance rs laevo-rotatory. The same order of phenomena will be observed if DETERMINATION OF THE ANGLE OF ROTATION. 101 we start from a position 180 from the first. In case, however, we do not know beforehand the direction of rotation peculiar to the sub- stance, the following considerations must be borne in mind : Sup- pose that the plane of polarization, having originally the direction AB (Fig. 24), is diverted to CD (at an angle of 30 from A B) by passing through an optically- active medium, the dark band will then appear when the index stands at 30 or 210, and the substance may either be dextro-rotatory, 30, or laevo-rotatory, 360 - 210 = 150. In most cases the side on which the smaller amount of deviation occurs is the true direction of the rota- tion. We cannot, indeed, be so guided when the smaller of the two angles exceeds 90, which, however, only happens with sub- stances having very high rotatory power, or in using tubes more than 2 decimetres in length. In these cases, the question can easily be decided by examining the liquid in a tube only half the length of that originally used, or by diluting the solution to half its strength. The deviation should then be only half of the original amount, and it is thus easy to discover which is the direction in which this holds. If, for example, darkness now occurs when the analyzer lies in the direction E F that is, at 15 and 195 the decrease shows the rotation to be dextro-rotatory, since the position measured for laevo-rotatory power would indicate an increase of rotation from 150 to 165, which is absurd. It is well to take observations on the filled tube at both positions, 180 degrees apart, as, owing to defective construction, the Nicol prisms may be somewhat eccentric, causing the observed angles to differ appreciably from each other. Any such source of error is accordingly eliminated by taking the mean of the two readings. Mitscherlich's instruments frequently have two opposite index arms, but as with fairly good graduation the difference between their read- ings does not amount to T l th degree, it is generally sufficient to use one. The differences between the angles in successive observations usually amount to several tenths of a degree, and the accuracy of the final result will, of course, be greater in proportion as the observa- tions are more numerous. As an example we may give the following results : 102 PROCESS OF DETERMINING SPECIFIC ROTATION. Half-circle I. Half-circle II. Empty Tube. (Zero -point). Filled Tube. Empty Tube. (Zero-point). Filled Tube. 0-2 16-4 180-4 196-3 5 16-2 6 3 4 15-9 3 6 2 16-0 5 5 3 16-2 6 6 Mean Rotation Angle o = Mean . . 0-32 16-14; 180-48 C 196-46' 15'82 C \ 15 '98 15-90 C Instead of the sodium flame, monochromatic light, obtained by placing a red glass slide in front of an ordinary gas lamp, was used by Biot and Mitscherlich. But in this way observation is rendered much more difficult through defect of brilliancy, besides which, t'he red light so produced does not correspond to any one distinct ray (see p. 46). 47. When white day or lamp-light is used with Mitscherlich's instrument, the angle of rotation observed is that for mean yellow rays, and, as already stated ( 18), is denoted by c^. For this purpose Fio . 25 the most suitable form is a gas or petroleum lamp, fitted outside its glass chimney with a metal screen coated inside with white porce- lain, and having a side opening (see Fig. 25). When with an empty tube placed in the instrument the analyzer is set to zero there appears, exactly as with the sodium flame, a dark band with fainter margins, which, as before, must be brought into the middle of the field of vision. If the active liquid is now placed in the tube, the different coloured rays composing this white light will experience different degrees of rotation, so that we shall have the phenomenon of rotatory dispersion. And here we may have two cases : 1. When the liquid possesses feeble rotatory power and the dispersion is therefore trifling, by turning the analyzer the dark band may be made to reappear with a border of blue on one side and red on the other. Now, if the blue border is to the left of the observer and the red to his right the substance is dextro-rotatory ; if vice versa, it is laevo-rotatory ; DETERMINATION OF THE ANGLE OF ROTATION. 103 and this independently altogether of whether the proper position has been found by turning the analyzer to the right or to the left. It is to be observed, however, that when a Mitscherlich instrument is provided with any kind of Galilean telescope, the foregoing conditions are reversed. The position of the dark band indicates the point of extinction of the yellow rays. 2. When, on the other hand, the rotatory power of the active liquid is high, the dark band appears broad and undefined, or else cannot be brought back by any movement of the analyzer at all. By turning the latter we get merely a succession of colours, produced by the analyzer extinguishing, according to the position of its principal section, certain of the unequally-rotated coloured rays, and allowing the rest to pass on with different intensities, thus producing a succes- sion of colour-mixtures. With solutions in which the angle of rotation for any ray is less than 90, the sequence of coloured tints, when the analyzer is turned from the initial zero-point, is as follows : IN L-ZEVO- ROTATORY LIQUIDS IN DEXTRO-ROTATORY LIQUIDS By turning the analyzer to By turning the analyzer to The Left. The Right. The Left. The Right. Yellow Yellow Yellow Yellow Green Orange Orange Green Blue Red Red Blue Red Blue Blue Red Orange Green Green Orange Yellow Yellow Yellow Yellow As a point of reference for the analyzer, that position is chosen where the transition from blue to red stands exactly in the middle of the field of vision. This being the point of extinction of the yellow rays, the observed angles will be cij. With substances of still higher rotatory and dispersive powers, intermediate tints make their appearance ; for example, between the blue and the red a reddish- violet, which, on the least touch of the analyzer, passes into one or the other. This is known as the sensitive or transition tint, and appears when the position of the analyzing Nicol is exactly such as to bar the passage of the mean yellow rays. This position also gives the angle Oj. For the relation between the angles of rotation a^ and a D see 18. Observations taken with white light cannot be made so exactly as those with the sodium flame ; the former light is therefore only employed when the latter is not available. 104 PROCESS OF DETERMINING SPECIFIC ROTATION. 48. Mitscherlwh's larger Instrument for Observations at Constant Temperature. In exact researches it is requisite, as already stated ( 22), that the temperature should not only be known, but be con- stant during the period of observation. This can only be effected by surrounding the tube with water. Moreover, in examining substances of feeble rotatory power, it is necessary to employ tubes of consider- able length, sometimes a whole metre long, to obtain rotation-angles of sufficient magnitude. Fig. 26 represents an instrument fulfilling these conditions, constructed at the works of Dr. Meyerstein, of Fig. 26. Gottingen, and in use in the chemical laboratory of the Polytechnic School at Aachen. Starting from the end next the light, the instrument consists of the following parts, resting loosely upon a frame formed of two strong iron bars Q Q : 1. A fixed tube A, containing the polarizing Nicol, a convex lens of long focus, and a diaphragm with a square aperture of 5 milli- metres side. Affixed to the same support as the tube is a circular dark screen, a, to shut off extraneous light. 2. A glass bottle with parallel walls J5, 1 filled with bichromate 1 May be obtained of Dr. J. G. Hofmann, 29, Rue Bertrand, Paris. DETERMINATION OF THE ANGLE OF ROTATION. 105 of potash solution, the object of which is to free the transmitted sodium rays from any admixture of blue or green light. This is important in the case of solutions of high dispersive power, as, with- out it, other tints make their appearance when the Nicols are crossed, and interfere with the sharp recognition of the dark band. 3. A sheet-metal case, C C, through which the solution tube passes, the ends passing water-tight through india-rubber corks. The tube in Fig. 26 is one metre long ; shorter tubes, of course, need cases of proportionate length. The case is filled with water, which is then raised to the desired temperature, usually 20 Cent., by moving about in it a hot bar, JT. For higher temperatures a Bunsen lamp with a row of burners, J J, must be used. 4. A support, Dj carrying a tube containing the analyzing Nicol, which, together with the graduated disc attached to it, is susceptible of movement round a common axis. This movement is communicated by the screw 6r, working in the toothed rim of the disc E. A small Galilean telescope, F, is fitted to the tube, the eye-piece of which must be so adjusted that the aperture in the diaphragm of the polarizer appears sharply denned. The support also carries two fixed verniers, and the divisions can be read off by the light of a small gas-jet, H. The sodium flame for the observations is obtained by means of the blow-pipe L, arranged vertically with chimney, M t over it, and connected by means of india-rubber tubing with the bellows P. Over the nozzle of the burner, and projecting from the support JV, is fixed a ring of platinum wire, which, when dipped in fused soda, imparts to the whole mass of flame an intense yellow, thus producing a strong light, essential for observations with great lengths of liquid, since the slightest opacity will, in such cases, often obscure the field so much as entirely to frustrate the experiment. The rotation- angles are determined in the same way as with Mitscherlich's smaller instrument. The analyzer is turned, by means of the milled head G, until the dark band appears exactly in the middle of the field of vision formed by the square aperture of the diaphragm, or, in other words, until the light spaces on each side of the dark band appear of equal width. The tube is first introduced empty, and the two zero-points determined, after which it is filled with the active liquid, the metal case being turned up on one end for the pur- pose. When shorter tubes are used, the intervention of extraneous light must be prevented by enclosing the course of the rays alter they 106 PROCESS OF DETERMINING SPECIFIC ROTATION. leave the tube with a paste-board cylinder, always taking care to have the polarizer and analyzer properly placed at the ends. The supports A and D can be slid along and screwed to the cross-bars in other positions as required. In all exact observations it is necessary to determine the zero- point afresh with each observation, as changes in the temperature of the place as well as differences of tension in the metallic screw-joints have an appreciable affect on the readings. The following values, obtained with a 10 per cent, solution of cane-sugar, are given as a working example : The zero-points were found at about 20 and 200 on the right and left sides respectively of and 180. The vernier could be read accurately to 0*1 and approximately to 0'01. The temperature of the solution was 20 Cent. OBSERVATION- SERIES a. Length of Tube 219-90 millims. OBSERVATION-SERIES b. Length of Tube 1000-60 millims. Half-circle I. Half -circle II. Half -circle I. Half -circle II. Empty Full Empty Full Empty Full Empty Full Tube. Tube. Tube. Tube. Tube. Tube. Tube. Tube. 20-55 5-25 200-45 185-38 20-40 311-55 200-60 131-75 54 25 49 . -50 45 65 40 80 38 23 55 38 40 72 42 85 48 33 50 28 55 78 50 75 40 25 59 53 42 60 55 70 39 20 55 50 50 65 57 72 C 42 30 44 35 55 55 40 85 55' 20 55 30 40 70 43 83 43 30 "45 n 30 50 80 60 75 47 33 57 40 40 77 60 85 20-461 5-264 200-514 185-392 20-457 311-677 200-507 131-785 a = 15-197 15-122 68-780 68-722 V / v^ ^ 15-160 For 1 decim. a = 6'894 C 68-751 For 1 decim. a = 6'871 C DETERMINATION OF THE ANGLE OF ROTATION. 107 (b.) Wild's Polariscope. 49. The polariscope invented by Wild 1 in 1864, which has already come largely into use, affords results considerably more accordant than those obtained by the apparatus of Mitscherlich. Fig. 27. Its novelty consists in the introduction of a Savart-prism 3 between the polarizer and analyzer (the former of which has the rotatory move- ment), whereby a number of parallel interference-bands are brought .into the field of vision, which vanish in certain positions of the polarizer. These positions, which can be determined with great accuracy, furnish the reference marks of the instrument. A sodium flame is used as the source of light. 1 H. Wild : Ueber ein neucs Polar istrobometet\ Berne, 1865. 2 [" Savart^ches Polariskop," see footnote, page 98. D.C.E,.] 108 PROCESS OF DETERMINING SPECIFIC ROTATION. The details of the instrument, as constructed by Hermann and Pfister, mechanicians, Berne, 1 are shown in Figs. 27 and 28, the same parts being indicated in Fig. 27 by small and in Fig. 28 by large letters. A metal stand X, Fig. 28, supports a brass cradle Y, which is capable of vertical and horizontal movement, and carries at its ex- tremities the polarizing and analyzing arrangements of the instrument. Entering at a, Fig. 27, into the dark chamber b, the light passes through a circular diaphragm c (10 millimetres in diameter), thus reaching the Nicol d. The latter is fixed to the graduated disc e t with which it turns on a common axis. Thence, the polarized ray, after traversing the solution-tube /, passes on to the analyzer. Here it meets, first, the so-called Savart polariscope, a prism g, composed of two plates of calc-spar 3 millimetres thick, cut at an angle of 45 to their optic axes, and cemented together with their principal sections crossing each other at right angles. To this succeed two- lenses forming a telescope of low power (about 5 times), the one, h, having a focal length of 120 millimetres, the other,/, of infinite length. Between the two, and in the focus of the objective h, is a circular diaphragm, A*, of about 4 millimetres diameter, provided with cross-threads. Lastly comes the JSTicol prism /, fixed with its principal section horizontal. The latter will therefore form an angle of 45 with the principal sec- tions of the double-plate g. That this relative position of the parts g and / may remain unaltered, the draw-tube, containing the Nicol and the lens i, is furnished with a guide-pin. The whole front part is set in the tube Z, which projects from the arm Y, and which allows it only a small movement about its own axis. For this purpose the tube is provided with a slot and adjusting screws m m, which clamp a pro- jection on the inner tube. The object of the arrangement is for fixing the zero-point. Lastly, at n is placed a circular screen to shade the observer's eyes from extraneous light. The mode of effecting rotation of the polarizing Nicol is as follows : The circular disc and the Nicol move in a piece within a fixed ring projecting from the arm ' Y. The disc is provided on the side next the observer with a toothed wheel driven by the pinion 0, worked by the rod q, with milled-head p. The graduation is close to the edge of the disc, and in front of it is a fixed vernier or simply an index arm r. To read off the divisions a telescope, s 9 is used, consisting of the movable eye- 1 Dr. J. G. Hofmann, 29, Kue Bertrand, Paris, and Schmidt and Haensch, Stall- schreiberstrasse 4, Berlin, also supply the instrument. DETERMINATION OF THE ANGLE OF ROTATION. 109 piece t and objective ", and having at the farther end, 0, an inclined metallic reflector with round hole in the centre, by means of which the light from a small gas-flame on a movable arm w, is thrown upon the vernier. In conclusion, it should be stated that the instrument is generally constructed for tubes 220 millimetres (8 '6 in.) long. 1 Should the instrument be wanted for general scientific work and not merely as a , it is necessary to take care that the disc be graduated all round, and not 110 PROCESS OF DETERMINING SPECIFIC ROTATION. 50. That the liquids may possess a fixed temperature maintained constant, the experimental tube requires to be laid in a water-bath. For this purpose it is enclosed in a metal jacket of considerabty larger diameter, so as to allow a current of water to flow between (see 65, Fig. 44). The complete arrangement of the apparatus ready for observation, is shown in Fig. 29. The instrument is set up opposite a Bunsen lamp B, which, with its bead of common salt, gives the sodium flame (or the lamp shown in 22, Fig. 46, may be used instead) . The outer case of the tube is provided with two side pieces, of which the lowermost is connected by india-rubber tubing, D, with the reservoir A, while the other at C serves as an outflow-pipe. A third opening, E, is for the insertion of a thermometer in the water as it flows through. The zinc reservoir A, resting upon a tall iron stand, is provided with a stirrer F t and is swathed in flannel to prevent loss of heat. One or two thermometers, G, serve to indicate the temperature of the water, usually maintained at 20, by means of the lamp H. The water is allowed to flow through the tube for about twenty minutes before the observations are begun, the stream being interrupted during observa- tion, while the thermometer E must remain steady throughout. The in- strument should be set up in a darkened room ; the gas-jet required for Fig. 30. reading the scale is controlled by the stop-cock /. At TTis represented a short (100 millimetre) tube, provided with a junction-piece to allow of its insertion in the instrument. 51. In carrying out observations a tube, empty at first in order to fix the zero-points is introduced and the eye-piece drawn out, so that the cross-threads appear sharply defined. The polar- izing Nicol must then be turned by means of the milled-head, p. 107, Fig. 27, until a number of parallel dark bands or. fringes make their appear- ance in the field of vision (Fig. 30, a). As the move- in one or two quadrants only. The instruments made by Hermann and Pfister have their discs divided to the third of a degree (20 minutes), and either a vernier to give readings to 5 minutes, or else a simple index-point which suffices to read to the same amount approximately. The polariscopes made by Dr. Hofmann, of Paris, read to single minutes. - It would be more convenient if the divisions on the scales were not minutes but decimals of a degree (as 0'02), as it is always in this form that the rotation angle of active substances is expressed. In reading as minutes one has to convert- into decimals of a degree by dividing by O'G. DETERMINATION OF THE ANGLE OF ROTATION. Ill ment continues these become fainter, until at last a position is reached at which a luminous space, devoid of lines, occupies the field. By a slight movement of the milled-head to and fro this luminous space is brought, as nearly as possible, into the middle of the field of vision, so that the remains of the fringes appear to stand at equal distances to the right and left of the cross-threads (see Fig. 30, b). This position serves as reference-point for the angular measurement. If the Nicol be turned further, the dark lines will grow darker till they attain a certain maximum intensity, then become fainter again, and again vanish ; these maxima recurring at intervals of 90 P in the course of a complete revolution. 1 Generally the dark lines exhibit certain peculiarities of form in each position which can be recognized. 2 Their disappearance indicates positions of the movable Nicol, in which its principal section either coincides with, or is perpendicular to the plane of the principal section of the first of the calc-spar plates of the Savart, while they occur with maximum intensity when these 1 For the theory of these interference -bands, see Wild, Polaristrobometcr, Berne, 186o ; or Wiillner, Lehrbnch der Physik, 3 Aufl. Bd. 2, 604. 2 In many Wild' s polariscopes the luminous space is too wide to allow any remains of the dark lines to show on the right and left of it. Some other reference position must then be chosen. Perhaps the best method is when the dark lines have nearly passed out of the field to fix the eye on one side of the field of vision, say, the right, and continue turning the analyzer slowly until the last traces of the lines disappear at that side. This position will necessarily be the same in every observation that is to say, the milled-head p will always have communicated to the polarizer precisely the same amount of adjustment in each case. The cross-threads are not required here. With many people, however, this method does not afford the same amount of accuracy as by bringing- the fringes into a position at equal distances from the cross-threads on each side. In the case of an instrument in which the luminous space is too wide, Tollens (Ber. der dcutsch. chem. Gesell. 10, 1405) adopts the plan of loosening the adjustment -screws and turning the ocular draw-tube, containing the stationary Nicol I, Fig. 27, through an angle of 20 to 40 on its own axis. In this way the phenomena presented by a com- plete revolution of the analyzer are altered, the field becoming more or less darkened at two points 180 apart, and acquiring at two intermediate points a maximum luminosity. The dark lines vanish at each position as before, but while in the illumined quadrants the luminous space is now broader, in the darkened quadrants it is narrower than before. The former positions are entirely unsuitable for purposes of observation ; but the two latter permit of a very sharp adjustment of the fringes in regard to the cross-threads. The observations must then be made in these two quadrants only. See, also, Tollens (Ber. der deuUch. chem. Gesell. 11, 1804). Some instruments are so constructed that the interference -bands appear vertical, in which case the cross -threads are placed horizontally. In Wild's instruments, should other lines appear crossing the field of vision obliquely, it is a sign that the principal sections of the two calc-spar plates of the Savart are not truly perpendicular to each other, and the instrument should be returned to the maker for readjustment. 112 PROCESS OF DETERMINING SPECIFIC ROTATION. two planes form angles of 45. The parts are generally so regulated by the maker that th exposition of the index at the absorption- points is approximately at the readings 0, 90, 180, 270 on the scale, admitting, however, of a certain amount of adjustment by means of the screws m m, Fig. 27. If the Nicol is set to one of the four zero-points, and the empty tube replaced by one filled with some optically-active liquid, the interference-bands reappear. In its passage through the active medium the plane of polarization of the transmitted ray is made to rotate through a certain angle, and to restore it to a position either parallel or perpendicular to the principal section of the first calc- spar plate of the Savart, the Nicol must be turned in the opposite direction to that in which the rotation has taken place, when the fringes will again disappear. The graduated disc must therefore be turned to the left if the substance is dextro-rotatory, and to the right if laevo- rotatory. But, as regards the movement of the milled-head P p, Figs. 28 and 27, inasmuch as a change of direction is involved in the wheel-and-pinion movement, the direction in which the milled-head is turned must be the same as that of the rotation. When, as usually happens, the graduation follows the same direction as the figures on a watch-dial, the readings for a dextro-rotatory substance will be greater, and for a laevo-rotatory substance less than the number on the disc at the zero-point. 52. If the direction of the rotatory power of an active liquid be unknown, it will be best to begin observations with a weak solution in the tube, so as to get a feeble amount of rotation. It will then be easy to see whether the direction is to the right or the left of the zero-point. On the contrary, when the rotation is considerable, a doubt may remain as to the direction, in the same way as with Mitscher- lioh's instrument ( 46). For instance, let the four zero-points be 90 180 270 and after the insertion of the tube with its liquid, the vanishing points of the dark lines, 30 120 210 300. Here the medium may be, as shown in Figs. 31 and 32, either dextro- rotatory with an angle of 30, or Inovo-rotatory with an angle of 60. To decide the question, a second observation is necessary with a shorter tube, or a more dilute solution. If the length of tube or DETERMINATION OF THE ANGLE OF ROTATION. 113 strength of the solution be half that in the former experiment, then also the angle of rotation will be the half only of that first observed. The vanishing points of the dark lines will then appear either at 15 105 195 285, as in Fig. 34, in which case the substance is dextro-rotatory, or at 60 150 240 330, as in Fig. 33, when it is laevo-rotatory. Fig. 31. Tig. 32, Fig. 34. Accordingly, if observations with the shorter tube or weaker solution give lower readings than the original, the rotation is right- handed, whilst if the readings are higher than at first, the rotation is left-handed. The conditions are, of course, reversed when the graduation of the instrument is towards the left. 53. In examining solutions of very high rotatory power it may happen that the angle of rotation exceeds 90, so that the read- ings are always found in the quadrant beyond. In such cases, to avoid error, the observations should be made with two tubes of 114 PROCESS OF DETERMINING SPECIFIC ROTATION. different lengths. For example, the following were, in round num- bers, the values obtained with laevo-rotatory nicotine, in a 100 millimetre tube : Quad. I. Quad. II. Quad. III. Quad. IV. Empty tube 90 180 270 360 Full " 18 108 198 _288 Angle of rotation 72 72 72 72 Apparently, therefore, a layer of nicotine 100 millimetres in depth rotates through an angle of 72. A second observation was now taken with a tube 50 millimetres long, when the following results were obtained : Quad. I. Quad. II. Quad. III. Quad. IV. Empty Tube 90 180 270 360 Full 9 99 189 279 Angle of rotation 81 ~81~ 81 81 Here the angle, instead of being reduced to half, as we should expect, is larger even than that given by twice the thickness of medium. If 50 millimetres of nicotine rotate through 81, 100 millimetres should rotate through 162. Now this is found to be the case when the zero- point of the observations with a tube of the last-named length is moved a quadrant to the right. We then get : Quad. Quad. Quad. Quad. Empty Tube II. 180 III. 270 IV. 360 I. 90 Full ' I. 18 II. 108 III. 198 IV. + 72(=360-288) Angle of rotation 162 162 162 162 The foregoing conditions are shown in Figs. 35 and 36, the former Fig. 35. Fig. 36. DETERMINATION OF THE ANGLE OF ROTATION. 115 of which shows the rotation for a length of 50 millimetres, the latter for 100 millimetres. 54. Wherever exactness is required, the observations should be repeated in each of the four quadrants of the circle. It will be found that appreciable differences exist between the angles of rotation thus obtained, differences which van de Sande Bakhuyzen 1 has shown originate in defective construction of the Nicol, as well as in improper placing of the two calc-spar plates of the Savart. These errors, however, disappear altogether when the mean of the four values for the angle of rotation is taken. When the observations are repeated in two opposite quadrants only, and the mean of the readings is taken, the compensation of errors is not indeed complete, but the degree of accuracy attained is usually enough for all ordinary pur- poses. The deviations from the true value do not exceed 0'03 at the most, and are generally less than 0'01. To take observations in two adjoining quadrants has not, of course, the same compensatory effect. To obtain very precise results, it is obviousty requisite that a still larger number of observations should be taken. As a rule, five observations in each quadrant will be enough, so that allowing for the verification of the zero-points, which should be repeated at least once each day on taking observations, the angle of rotation finally obtained will be the result of forty readings. Where considerable differences are found in the readings, the number of observations must be increased. 3 This will occur when the solutions are not abso- lutely clear ; slight colorations, on the other hand, do not materially affect the observations. The degree of accuracy attainable is shown in the two series of observations appended. These were taken with an instrument of Hermann and Pfister's manufacture, graduated to divisions of 5 minutes, and allowing of approximate reading to single minutes. The liquid employed was an aqueous solution of cane-sugar containing 19'4-3 grammes in 100 cubic centimetres. The length of tube was 21979 millimetres. 1 van de Sande Bakhuyzen : Pogg. Ann. 145, 259. 2 Differences of 20 minutes in the readings may easily occur with unpractised observers, but with care these can soon be much reduced in amount, so that a hasty opinion should not be formed of a newly-purchased Wild polariscope. When the observer has become accustomed to the instrument, and the latter is properly con- structed, the difference in the readings will seldom exceed 5 minutes. i 2 116 PROCESS OF DETERMINING SPECIFIC ROTATION. OBSERVATION -SERIES A. Quadrant I. Quadrant II. Quadrant III. Quadrant IV. Empty Full Empty Full Empty ' Full Empty Full Tube. Tube. Tube. Tube. Tube. Tube. Tube. Tube. j i >% 20' 28 40' 90 15' 118 40' 180 10' 208 35' 270 18' 298 50' - 24' 46' 20' 45' 17' 35' 15' 45' 18' 43' 20' 45' 15' 45' 20' 45' 20' 45' ' 18' 38' 15' 43' 18' 48 t 18' I 45' 22' 32' 12' 35' 18' 4G' 020-0' 28 43-8' 90 19-0' 118 40-0' 180 13-8' 208 38-6' J 270 17-8' 2984G-8' j a = 28 23-8' 28 21-0' 28 24-8' 28 29-0' or= 28-397 28-350 28-413 28-483 Mean of Quadrants I. and III. 28 24-3' = 28-405. II. IV. 28 25-0' - 28-417. L, II., III., IV. 28 24-65' = 28-411. OBSERVATION -SERIES B. 018' 28 50' 90 18' 118 45' 180 18' 208 38' 270 20' 298 42' 22' 42' 15' 35' 15' 34' IS' 45' 25' 45' 15' 32' 12' 40' 20' 47' 17' 42' 20' 40' 12' 40' 19' 54' 20' 44' 22' 42' 15' 40' 16' 48' 020-4 / 28 44-6' 90 18-0' 11838-8' / 180 14-4' 20838-4' / 270 18-6' 298 47-2' 1 a = 28 24-2 N/- 28 20 -8' 28 24-0' 28 28 -6' or = 28-403 28-347 28-400 28-477 Mean of Quadrants I. and III. 28 24-1' = 28'402. II. ,, IV. 28 24-7' = 28-412. L, II., III., IV. 28 24-4' - 28-407. DETERMINATION OF THE ANGLE OF ROTATION. 117 (c.) Half- Shade Instrument (Polar imetrcs a Peiiombre) of Jellett y Cortiu, and Laurent. In these instruments the mechanism for sensitiveness is arranged to produce a circular field of vision divided into halves, which in certain positions of the analyzing Nicol are unequally illuminated, but in one particular position exhibit a uniformly faint shade. This position, which can be fixed with great accuracy, is taken as the point of reference. The use of monochromatic sodium light is pre-supposed. 55. The earliest instrument of this kind was constructed by Jellett in I860. 1 In this, between the polarizing and analyzing Nicols, and close behind the former, is placed a prism of peculiar form. An elongated rhombohedron of calc-spar which, by grinding the ends, has been converted into a right prism, is divided longitudinally into halves by a plane nearly, but not quite, perpendicular to its prin- cipal section, and the two halves then reunited, but in reversed positions. The prism is mounted in a case, furnished at the extremities ^ with diaphragms having circular apertures. The circular field so obtained appears divided diametrically by the section into equal , halves, in which the planes of polarization are slightly inclined to v?*' each other. A plane polarized ray passing through can, by turning t the analyzer, be extinguished by either half of the prism, these points ,/ of extinction lying very close together, whilst between them lies the position of uniform shade. The appearance of uniform shade can also be made to vanish by the introduction of an active liquid, and, to bring it once more into view, the analyzer must be turned on its axis through a certain angle, which can be taken as measure of the deviation of the ray produced by the active substance. 56. Cornu's instrument 2 consists of an ordinary Nicol as analyzer, with a polarizer of peculiar construction. The latter is formed out of a Mcol prism, by bisecting it in the direction of the plane passing through the two shorter longitudinal diagonals, cutting down the sectional faces 2| and reuniting the halves. In this way we have a double Nicol prism, having its two principal sections form- ing an angle of 5 with each other. .When, therefore, by turning 1 Jellett : Reports of the British Association, 1860, 2, 13, 2 Cornui Butt. Soc. Chim. [2], 14, 140, 118 PROCESS OF DETERMINING SPECIFIC ROTATION. the analyzer, we bring its principal section exactly perpendicular to one of the two principal sections of the polarizer, perfect obscura- tion follows in the corresponding half of the field of vision, the other half remaining illumined. A rotation of 5 reverses these conditions, the dark half then becoming bright and vice versa, while midway between these two positions lies a point where the halves exhibit equal degrees of incipient shadow. Fig. 37. Fig. 38. 57. The half- shade instrument, however, which has come into most general use is that of Laurent, 1 of which a representation is given in Figs. 37, 38. 1 Laurent: Dingier' s Polyt. Journ. 223, 608. DETERMINATION OF THE ANGLE OF ROTATION. 119 In this, 1 the light from a sodium flame passes through the following optical apparatus : 1. A thin plate, a (Fig. 37), cut from a crystal of bichromate of potash, serving to free the yellow ray from intermixture of green, blue, and violet light. This is enclosed between a couple of glass plates and fixed in a movable diaphragm. 2. A double refracting calc-spar prism, b, as polarizer. These two pieces are placed one at each end of the tube A B, Fig. 38, which is inserted in the fixed portion C C', of the instrument, within which it is capable of rotation through a small angle. The amount of this movement is regulated by means of the screw-stop /3, passing through the slot at C. 3. A circular diaphragm c, containing a glass plate, to which is affixed a thin plate of quartz, cut parallel to the axis, and just large enough to cover exactly one half of the circle. The thickness of the quartz plate must be so regulated that the yellow 'rays polarized parallel and perpendicularly to the axis may in their transmission undergo a retardation of half a wave-length. (In an instrument manufactured by Dr. Hofmann, of Paris, the thickness of this quartz plate is Oil millimetre.) 4. The solution-tube d. 5. An analyzing Nicol c, furnished with rotatory movement. 6. The lenses /and #, forming a small Galilean telescope. The analyzer rotates in a piece with the divided disc E, within the stout ring, M. For this purpose, the back of the disc is furnished with a bevelled toothed wheel, driven by a small pinion worked by the milled-head F. The vernier is screwed firmly to the arm G, hanging down over the graduated edge of the disc. In read- ing, a magnifier, H, is used, which has a motion round the point O, and is provided at the top with a metal reflector, J. The latter can be made to reflect light on the divisions either from the sodium flame or some other convenient source. The Nicol can be turned in its case slightly by means of the screw L, so as to alter the zero-point. The telescopic lenses are mounted in tubes, K N, the latter of which has a draw motion. The graduated circle, a front view of which, with the parts pertaining thereto, is given in the figure, has a diameter of 250 millimetres, and the vernier reads to single minutes. The optical 1 May be obtained of Dr. Hofmann, 29, Rue Bertrand, Paris ; Schmidt and Haensch, Berlin; J. Puboseq, 21, Rue de POdeon, Paris; Bartels and Diederiche, mechanicians, G-ottingen. Fig. 38 is drawn from one of Hofmann's instruments. 120 PROCESS OF DETERMINING SPECIFIC ROTATION. arrangements are fixed at the ends of a brass trough, of semi-circular section, D, resting on the stand P. The size of the trough should be such as easily to take tubes 3 decimetres long with their water jackets. 58. The peculiar feature in Laurent's instrument is the thin plate of quartz PQ, cut parallel to the axis, Fig. 39. Let the polarizer Fig. 40. Fig-. 41 Fig. 42. B be first so adjusted that the plane of polarization of the transmitted pencil of light is parallel to the axis of the plate that is, lies in the direction A B the two halves of the field of vision will then appear equally dark or equally bright in every position of the analyzer. But if the polarizer be inclined to A B, at an angle a, the plane of polari- zation of the rays passing through the quartz plate will undergo deviation through an equal angle, a, in the opposite direction. Therefore, when in the uncovered half the plane of polarization has the direction AC, in the covered half it will have the direction A C'. If now we turn the analyzer, then, according as its plane of polari- zation lies in the direction c c or cV, so will either the rays polarized parallel to A C or to A C' be extinguished, and the corresponding half of the field of vision will appear completely dark, while the other half merely suffers a partial decrease of brightness (Figs. 40, 41). In the middle position, b b, Fig. 42, there is a uniform shading over the two halves, but a very slight movement to and fro of the analyzer will at once destroy the equality. These phenomena repeat themselves when the analyzer has been moved through an angle of 180 . 1 The degree of uniform shade obtained by bringing the analyzer into the middle position will be greater, the smaller the angle a (Fig. 39), which the plane of the polarizer makes with the axis of the quartz plate. The parts are set by the instrument-maker so that these two 1 For the theory of the phenomena produced by polarized light with plates cut parallel to the axes of uni-axial crystals, see Wiillner's Lehrbiwh der Physik, 3 Aufl. Bd. II. S. 568. Laurent, in his earlier instruments, employed a thin plate of gypsum instead of the quartz, which gave the same results (Comptcs Rend. 78, 349). DETERMINATION OF THE ANGLE OF directions are parallel to one another, but, as before observ( adjustment is arranged for by allowing the polarizer a slight amount of rotation, by means of the ring B, in the slot /3, Fig. 38, whereby the field of vision is brightened. In this way the sensitiveness of the instrument can be altered. This is always greater the smaller the departure from the parallel position, when, consequently, the less will be the amount of movement of the analyzer requisite to produce perfect obscurity of one or other half of the field of vision. The deepest shading suitable should therefore be chosen. 59. In setting up the instrument it is directed towards a sodium flame, and the telescopic eye-piece so adjusted that the edge of the quartz plate appears to divide the diaphragm by a sharply defined vertical line. The analyzing prism must then be turned until both halves of the field of vision appear equally dark, and the polarizer adjusted to that position where the least displacement of the analyzer is required to produce an appreciable change in the appearance of the field. In determining the zero-point, the analyzer is brought into the middle position, where the partition -line becomes invisible. More- over, it is better to fill the experimental tube with water, so as to equalize the conditions in respect to absorption of light with those holding in observations of active liquids. One can then make the actual zero-position correspond as nearly as possible with the zero- mark by means of the screw L (Fig. 38). Then, introducing the liquid, a rotation of the analyzer with its disc to the right will be necessary to restore the reference position if the substance be dextro- rotatory, and to the left if it be Ia3vo-rotatory. If now, owing to colouring or any slight turbidity, the field of vision is too dark, greater brightness can be obtained by a slight movement of the polarizer on its axis (see 58), but this entails the disadvantage that larger movements of the analyzer are then required before any alteration on the uniformity of shade is apparent, and the readings accordingly are more divergent. In clear solutions these do not differ by more than single minutes. For determining the direc- tion of rotation in active substances of high rotatory power, the procedure given under the head of Mitscherlich's instrument ( 46) is equally appropriate here. , A bright sodium flame is necessary, which is best obtained by using the lamp shown, 46, Fig. 22. If tubes provided with water- 122 PROCESS OF DETERMINING SPECIFIC ROTATION. jackets are employed, the complete arrangement of the instrument corresponds exactly with the description given 50, Fig. 29. To eliminate errors in the Nicols, the observations should be made at two positions 180 apart, and the mean taken. The subjoined table con- tains, as an example, a series of observations with one of Hofmann's instruments, graduated from both ways to 180. The zero-point was approximately at 90 in each half circle. The active liquid was a solution of cane-sugar : Tube with Water. Tubes with Sugar Solution. Zero-Point. Observation- Series a. Observation- Series b. Tube Length 200 48 mm. Tube Length, 300*08 mm. Half Circle I. Half Circle II. Half Circle I. Half Circle \ Half Circle II. I. Half Circle II. 89 54' 89 56' 103 44' 76 10' 110 32' 69 14' 53' 57' 42' 9' 35' 11' 56' 55' 45' 5' 36' 10' 57' 55' 39' 5' 31' 15' 59' 55' 46' 4' 33 12 52' 59' 41' 7' 33' 16' 54' 54' 38' 10' 32' 13' 57' 56' 40' 5' 30' 15' 56' 56' 41' 9' 35' 16' 56' 56' 42' 7' 31' 14' 89 55-4' 89 55-9' 103 41-8' 76 7-1' , 110 32-8' 69 13-6' 103 41-8' 89 55-9' 110 32-8' 89 55'9' Observed Angle of Rota- tion a Mean a = 89 55-4' 76 7-1' 89 55-4' 69 13-6' 13 46-4' 13 48-8' 20 37-4' ^ -s_ 20 42-3' = 20-664 13 47-6' = 13-793 20 39-85' For 1 decim. a, = 6-880 6-886 (d.) Comparison of MitscherlicJi's, Wild's, and Laurent's Instruments. 60. To determine the degree of concordance possible between DETERMINATION OF THE ANGLE OF ROTATION. 123 the above instruments,, observations were made with the same tubes on two suitable solutions of sugar. In each case, forty readings were taken, one-half of which were for the determination of the zero- point. The following were the results : Instrument. Solution I. Solution II. Tube Length 219-79 mm. Angle of Rotation for 100 mm. Tube Length 220-00 mm. Angle of Rotation for 100 mm. Mitscherlich Wild Laurent 20-227 20-285 20-268 9-203 9-229 9-222 14-570 14-574 14-602 6-623 6-625 6-637 From this it will be seen that the results obtained with these several instruments agreed to the tenth of a degree, the variations not appearing till the second, and in some cases not before the third decimal place. It is therefore immaterial which instrument is used, any superiority consisting merely in the comparative facility with which observations can be made. An idea of the amount of difference that may be expected between the results obtained by different obser- vers is shown by the following table, in which are recorded the angles of rotation obtained with the same sugar-solution by two observers of almost equal experience in the use of the three several instruments : Polyscope L ^;' used -IT in milbm. Observed Angle of Rotation. Angle of Rotation for 1 decim. Differ- ence, A-B. Observer A. 15-165 68-809 Observer B. Observer A. 6-896 6-876 Observer T> Mitscherlich j 219-89 ) 1000-60 15-160 68-751 6-894 6-871 + 0-002 + 0-005 Wild ( 99-92 j 219-79 6-941 15-171 6-849 15-078 6-947 6-903 6-854 6-860 + 0-093 + 0-043 Laurent M M i 200-48 \ 300-08 3an 3an error in a 13-786 20-628 single deter 13-793 20-664 6-876 6-874 6-895 0-028 6-880 6-886 - 0-004 - 0-012 miiiation 1 6-874 0-015 + 0-021 Here we see the observations of the two observers varying within limits of hundredths or even only thousandths of a degree. 1 Mean error for a single determination = A/ ' _\ ' ~ ' wnen S l 8, . . . 8 n represent, the differences between individual observations and their arithmetical mean, and n the number of observations taken. 124 PROCESS OF DETERMINING SPECIFIC ROTATION. The variations that occur in observations with different tubes are similar in amount, provided indeed that, as in the above instances was the case, their lengths have been measured correctly to within 0-05 millimetre. (See further 75.) (e.) Determination of the Angle of Rotation for different Rays. [METHOD OF BROCH.] 61. The instruments thus far described serve only to measure the rotation of the yellow sodium ray D. It is possible, indeed, at least with Mitscherlich's and Wild's instruments, by introducing into the flame, instead of common salt, some other substance, such as lithium or thallium compounds, to produce monochromatic light of another colour. The red lithium flame has the disadvantage of being too weak in illuminating power to admit of exact observations ; besides which, it retains an admixture of yellow rays, which, however, can be absorbed by placing a red glass slide in front of the flame. The volatility of thallium compounds, on the other hand, renders it difficult to maintain the green-coloured light with sufficient intensity for any length of time. 62. A method which admits of the determination of the rotation for a whole series of rays of known wave-length was proposed by Broch in 1846 1 , and about the same time by Fizeau and Foucault, 2 and has since been adopted by various other observers, as Hoppe- Seyler, Wiedemann, &c. For this purpose, solar light is employed, reflected horizontally by means of a heliostat into a darkened chamber. The beam passes in succession through (a) a polarizing Nicol ; (b) the layer of active substance ; (c) the analyzing JNficol: (d) a spectroscope, consisting of a collimator, prism, and telescope, which last must be furnished with cross- threads. If, leaving out the liquid, the analyzer is first adjusted to the position of greatest darkness the zero-point and the active liquid then introduced, the spectrum with Fraunhofers lines will at once appear in the telescope. If the analyzer be then rotated, a position will be found at which a vertical black line makes its appearance, and can be made to move across the field of vision by continuing the rotation. This is caused by the Nicol as it revolves, extinguishing in succession the rays whose planes of polarization are perpendicular to its own. If the cross- 1 Broch: Dove's Rcpertorium d. Physik. 7, 113. 3 Fizeau and Foucault : Comptcs Rend. 21, 1155. DETERMINATION OF THE ANGLE OF ROTATION. 125 wires of the telescope have been previously made to coincide with some one of the Fraunhofer lines, and the dark band be now brought to cover it, the reading on the graduated disc will give the angle of rotation for that particular ray. In a similar manner the amounts of rotation can be determined for other portions of the spectrum. 63. Instead of solar light, the use of which is of course very much restricted, artificial light may also be employed for this method of observation. Y. von Lang's 1 method of using lithium, sodium, and thallium light, is first to adjust the cross-lines of the telescope upon the lines produced by volatilizing a salt of the respective metal in a Bunsen burner ; then, replacing the Bunsen by the luminous flame from an Argand, to bring into view the continuous spectrum necessary for the production of the dark absorption- band. By rotating the Mcol until the band is made to coincide with the cross-threads the position of which must, of course, remain undis- turbed during the experiment the angle of rotation for the given ray is obtained. In the same way the light from a hydrogen Geissler- tube can also be used. By these means it is possible to determine the angle of rotation for six different rays of known wave-length. In the subjoined table 'these artificial lines are collated with the Fraunhofer lines so as to indicate their position in the spectrum. 2 Artificial Lines. Fraunhofer Lines. "Wave-length, in millim. A 0-0007607 S 0-0006872 Red lithium line Li a 0-0006712 Red hydrogen line H a C 0-0006567 Yellow sodium line Na D 0-0005893 Green thallium line Tl 0-0005350 E 0-0005271 b 0-0005182 Green -blue hydrogen line H0 F 0-0004862 Blue -violet hydrogen line H^, 0-0004343 0-0004304 H 0-0003956 v. Lang: Pogg. Ann. 156, 422. The wave-lengths of the Fraunhofer lines given above (of which C coincides with 126 PROCESS OF DETERMINING SPECIFIC ROTATION. The arrangement of the apparatus is shown in Fig. 43. It consists of a Mitscheiiich polariscope, with its polarizing Nicol at Fig. 43. a, and its analyzing Nicol, with rotatory motion, at c ; in front of it a spectroscope, consisting of a collimator, d, a prism, e, and a movable telescope,/ Instead of the usual cross-threads, the telescope is fitted H , D with Na, and JFwith H0), and also of line Hy, are the means of the results obtained by Fraunhofer, van der Willigen, Ditscheiner, Angstrom, Stefan, and Mascart (Wullner's Lehrbuch der Phys. 3 Aufl. 2, 136 and 141). For Li a and Tl Ketteler (Beobachtungen uber die Farbenzerstreuung der Gase, Bonn, 1865) gives the values 6706 and 5345, that of Na being taken as 5888 ; so that putting Na = 5893, we obtain the values Li = 6712, and Tl = 5350. The lines of other metals might probably be made available, as the following : Wave-lengths in millimetres. Red potassium line .. 0*0007607 Red cadmium line . . 0-000644 Green cadmium line . . 0-000534 Green magnesium line . . 0-0005182 Blue cadmium line . . 0-000468 Blue strontium line .. 0*0004607 Blue-violet cadmium line .0-000441 Violet indium line 0-0004101 (Fraunhofer line A}. (Hurion) . ( ) (Fraunhofer line b}. (Hurion) . (Lecoq de Boisbaudran) . (Hurion) . (Lecoq de Boisbaudran). Hurion (Pogg. Beibldtter, 2, 83). Lecoq de Boisbaudran (Spectres lumincux, Paris, 1874). DETERMINATION OF THE ANGLE OF ROTATION. 127 with two parallel vertical threads, separated from each other by a distance somewhat greater than the breadth of the black absorption- band. The determination of the angle of rotation of a given sub- stance comprises the following operations : 1. The determination of the zero-point of the analyzer. The spectroscope is removed, and the experimental tube left empty or filled with water. The Argand lamp i serves as the source of light. 2. The spectroscope is set up in its place, and in front of the Xicol a, the source of light h, which gives the lines (a Bun sen burner, with a bead of salt or a hydrogen tube) ; the analyzer is then rotated till the light can pass through. After widening pretty considerably the slit of the col- limator d, the telescope f is moved horizontally until the bright line under examination lies accurately between the parallel threads, when the clamp-screw g is tightened. This position of the telescope can be more readily found when the Argand lamp i, with a small flame, is placed behind the Bunsen burner h, so that the threads stand out against a bright background. 3. The tube containing the active liquid is then laid in its place, the Argand light turned full on, and the analyzer moved on its axis until a broad dark band, with faint edges, appears in the field of the telescope. This also is brought between the parallel threads, and the angle read off on the graduated disc. Lastly, by reproducing the bright line again, it can be ascertained whether the position of the telescope has been disturbed in the meantime. In observing the parts of the spectrum which lie near the ex- tremities, as the red lithium-line, the Drummond lime-light should be used for the production of the continuous spectrum, the Argand being too weak in red rays sufficiently to illumine the edges of the dark band. The above method does not admit of the same degree of con- cordance of results as when the polariscope is used alone, the posi- tion of the dark absorption -band being less definite, owing to the indistinctness of its edges. Thus von Lang, in the paper referred to, gives the following table as showing the varying positions of the analyzing Nicol in a determination of the rotatory powers of a quartz plate. Observation-series 1 and 2 were obtained with an Argand lamp, 3 and 4 with a Drummond light, the position of the polarizer in the second being different from that in the first two series. The tem- peratures of the quartz plate are also given in the table ; these exhibit 128 PROCESS OF DETERMINING SPECIFIC ROTATION. certain variations, but too small in amount to account for the differences in the observed positions. 1 2 3 4 Sodium Line. Thallium Line. Sodium Line. Lithium Line. Temp. Angle. Temp. Angle. Temp. Angle. Temp. Angle. 17-8 72-23 20-0 69-28 19-0 91-81 22-0 102-65 ,20-1 71-53 20-1 70-20 17-0 93-53 20-5 103-15 20-0 70-29 19-7 68-12 19-4 93-37 21-5 103-57 20-4 72-14 20-0 68-73 20-0 92-89 18-3 103-71 20-1 71-90 20-5 69-62 19-5 93-33 19-6 104-03 21-0 71-11 20-6 68-82 20-0 93-08 20-0 103-15 21-7 71-20 19-9 102-64 20-2 71-49 20-2 69-19 19-1 93-00 20-3 103-27 0-25 0-20 ' 0-25 + 0-20 B. Measurement of the Length of Tubes and their Adjustment. 64. The experimental tubes of polariscopes should invariably be made of glass. They are generally 2 decimetres (about 8 in.) in length, but shorter ones, 1 decimetre, and longer ones, 3 decimetres and upwards in length, can be used where the construction of the instrument will admit of it. The internal diameter varies from 6 to 10 millimetres (-^-in. to J~in.), and the thickness of the glass walls should be about 2 millimetres. The extremities are ground flat with great care, the ground surfaces being kept as nearly as possible perpendicular to the axis of the tube, otherwise it will be impossible to determine the length of the tube with any exactness. More- over, it is convenient to have the internal walls of the tube ground with coarse emery powder, so as, by dulling the surface, to prevent disturbing reflections. The mode of closing the ends of the tubes usually adopted is, as shown in Fig. 44, by plane parallel glass plates, which can be fixed down by a screw-cap, having a washer of india-rubber or soft leather between. As Scheibler 1 first observed, this mode of closing J Scheibler: Her. d. deutsch. chem. Gescll. 1868, 268. MEASUREMENT AND ADJUSTMENT OF TUBES. 129 the tubes may prove a source of error owing to the tendency of the glass plates under pressure to become double-refracting, whereby light passing through them is circularly-polarized. Moreover, when differences of tension exist in the body of the glass, owing to imper- fect annealing, the same results will appear altogether apart from pressure, although the latter intensifies them. Indeed, by applying sufficient pressure to the glass plates, the errors thus arising may even amount to several degrees. It will be evident then how essential it is that all new glasses should be carefully tested, before they are taken into use. For this purpose a series of observations should be made of the zero-point of the instrument, first with a tube open at the ends, then with a glass plate applied to one end under moderate pressure. Moreover, as the glass may be differently affected at different parts, the tube should be turned about on its axis so as to test every part. Generally speaking, if one glass is found to be circular-polarizing, all others of the same lot, cut at the same table, will prove to be so likewise. 65. The tubes supplied with the apparatus are usually fixed within a simple brass tube, or they may be left uncovered ; in either case the liquid inside will be exposed to the temperature of the sur- rounding air. JNTow as (see 22) the rotatory power of most substances is materially affected by heat, it is necessary to be able to control the temperature of the solutions during the continuance of the obser- vations. This can be done by enclosing the tube in a jacket of brass, 4 to 5 centimetres wide, and allowing water to flow between, supplied by a reservoir in which it has been previously raised to the desired temperature. Fig. 44 represents a tube enclosed in a Fig. 44. water-bath of this description. The glass tube a is fastened within the brass necks b b with shellac. The openings c c serve for the inflow K 130 PROCESS OF DETERMINING SPECIFIC ROTATION. and outflow of the water ; d is an opening to receive a thermometer. The mode of using the whole apparatus is given in describing Wild's polariscope ( 49, Fig. 29). Another arrangement is that adopted in Mitscherlich's large instrument, shown in 48, Fig. 26, in which the observation-tube is enclosed in a rectangular metal box filled with water. Or, lastly, the method shown in Fig. 45 may be adopted, in which the tube is laid round with a fine *. 45. lead spiral through which the water is allowed to flow ; the tube itself being pro- vided with two side openings through which the liquid is filled and emptied, and which serve also to hold the thermometers. } The two terminal plates can in this case be fixed permanently in their places, for which purpose a solution of isinglass in acetic acid may be used. To prevent loss of heat the lead tubing should be protected by wrapping round it a good layer of flannel. 66. Measurement of Length of Tube. In the formula for the determination of specific rotation, the length of tube appears as an absolute quantity, so that to render results obtained by different observers comparable, it is necessary to have a uniform standard of measurement ; and for this purpose, the first consideration is that the millimetre division on the measure be rigidly accurate. The determination of the tube-length is frequently left to the instrument-maker. As a means of verifying the ordinary 1 and 2 decimetre tubes, Scheibler 1 recommends round brass rods, made accurately 100 and 200 millimetres respectively in length, with flat ends. Screwing a glass plate on one end of the tube, the rod is pushed inside the open end, taking care that it stands straight, and the other glass plate put on, when, if the tube is of the proper length, it should fit exactly, and no room be left for the rod to move about when the whole is shaken. In all exact experiments, it is necessary to know the length of tube to within at least O'l millimetre, and it is therefore desirable to be able oneself to measure it with this degree of precision. Fig. 46 represents an instrument constructed by Feldhausen, mechanician, Aachen, for this purpose, which can be used for ordinary tubes of any Scheibler: Zeitschr.de* Vereins filr Riibcnzuckerindnstric, 1867,226; 1874, 786. MEASUREMENT AND ADJUSTMENT OF TUBES. 131 diameter, as well as for those provided with water-bath surroundings. On two supports AA (A in the side elevation) is fixed, horizontally, the brass bar BB, 3i decimetres in length, carrying the plate C fixed at one extremity, and the sliding-piece D. The latter consists of the piece a, which can be firmly clamped by the screw c, and is connected by means of the micrometer-screw d and the spring e with the second piece b, so as to communicate to the latter a fine movement. The bar BB is graduated to millimetres, and the sliding-piece b carries a vernier, reading to ^-th millimetre. Into the face of the fixed plate C Fig. 46. 1 k' E and the opposite face of the sliding-piece b, are screwed horizon- tally two round steel pins m n, to serve as supports for the tube we wish to measure E (which in the Fig. is shown as jacketed). Above the pin m is a wedge of steel/ fixed with its sharp edge vertical, against which one end of the tube is made to rest. A similar steel wedge g, is affixed to the short arm of the bent lever h i, which works on the pivot k ', these parts (indicated in the side-view by g h' i' k r ) being in con- nection with the sliding-piece b. The outside of the longer arm, i, which is directed downwards, has a spring p resting upon it, which tends to make it move towards the left ; and at its extremity an index mark q is placed which can be made to coincide with a similar mark on b. In using the instrument the pins m n are first removed by un- screwing, and the sliding-piece D pushed close up to C, until the two edges of the prisms / and g nearly meet. The part a is then clamped, and with the aid of the micrometer-screw d the part b i moved forward, until by perfect contact of the edges / and g, the index mark q, which at first stood to the left, is made to coincide with the murk on b. This gives the zero-point. The pins m n are then screwed K 2 132 PROCESS OF DETERMINING SPECIFIC ROTATION. into their place, D being pushed back far enough to allow of the tube to be measured, being suspended freely upon the pins. One end of the tube is pressed against the edge/, while the contact of g with the opposite end is completed with the micrometer-screw, until the marks at q again coincide. The length is then read off with the vernier on the graduated bar. Since the annular end-surfaces of the tube are never truly parallel, the latter should be turned on its axis through a quarter, half, and three-quarters of a circle, and the mean of the measurements in the several positions taken as the true length. Where a cathetometer is available, the following mode of deter- Fig. 48 mining tube-lengths may also be adopted. A piece of glass tubing a b (Fig. 47), of such diameter that it will slide easily inside the tube to be measured with- out shaking about in it, is closed at one end 1) with the blowpipe, the glass being drawn to a blunt point, which can then be sharp- ened off a little with the file. Enough is cut off the open end to leave the tube some millimetres shorter than the tube to be mea- sured, after which it is filled with mercury to about one- fourth of its length, the metal being retained in its place by a cork c pressed down on its surface. Into the mouth of the tube is inserted a close-fitting, well- greased piece of india- rubber tube d, through which passes a glass rod e, of diameter just sufficient to move easily within the india-rubber collar. To allow escape of air the india- rubber should be slit down its whole length at one side. The ends of the glass rod are drawn out a little, that at / being brought to ESTIMATION OF PERCENTAGE COMPOSITION OF SOLUTIONS. 133 a point. The other end is passed through the cork g, so as to ensure straight motion within the tube, and the rod is pushed down so far that the total length of the combination is somewhat greater than that of the tube to be measured. The latter is then closed at one end with glass plate and screw-cap, the contrivance just described slipped into it, and the glass rod pushed down by pressing the point / with the other glass end, and screwing the latter firmly down. The lower screw-cap is now removed, the inner tube withdrawn without dis- turbing the position of the rod, and fixed in gimbals (Fig. 48), whereby the weight of the mercury in the bottom keeps it truly per- pendicular. By means of a cathetometer the distance between f and b can then be determined. Repeated measurements taken in this way are found to agree with a mean variation of only + 0'02 millimetre. Where the apparatus is too wide and requires steadying in the tube, india-rubber bands, h h (Fig. 47), can be slipped over it. In determining the angle of rotation of a liquid at different temperatures, the consequent variations in the length of tube must be taken into account. For this purpose it will be found sufficient to take the mean value 0*0000085 as the coefficient (3 of linear expansion of glass for 1 Cent. Representing the length of tube in millimetres by L^ and the temperature of measurement by t t the length at any other temperature t' will be given by the formula L t , = L t \l + ft (t f - 0], when t > t, or L t , = L t [l ft (t 01 when t' < t. Thus if a tube measures exactly 200 millimetres, at a tempera- ture of 20, it will measure 200'02 millimetres at 30 and 199'98 millimetres at 10. The correction is therefore only needed for great variations of temperature and long tubes. 0. Estimation of Percentage Composition of Solutions. 67. Preparation of Solutions by Weighing the Active and In- active Constituents. For this purpose small blown glass flasks (Fig. 49) of 25 to 100 cubic centimetres capacity, with wide necks, and provided with ground-glass stoppers, will be found most suitable. The active substance is first weighed into a flask of this kind, after which the calculated amount of solvent necessary to give the desired percentage is introduced by means, first, of a wide, and subse- 134 PROCESS OF DETERMINING SPECIFIC ROTATION. quently a narrow-necked pipette. But as in this way a drop or two may be easily added too much, and thus the right percentage not accurately attained, it is best to prepare the solutions roughly at first by weighing in a pair of scales, and afterwards determine accurately by a chemical balance the real amount added. 1 iu-. 49. 68. The percentage composition of fresh-prepared solutions can easily be found to the third place of decimals by weighing to milligrammes, but this accuracy vanishes when it becomes necessary to filter from turbidity, the evaporation of the solvent which takes place during the process, increasing the percentage of non- volatile active sub- stance. To estimate the magnitude of the error arising from this source, a few experiments were made partly by placing the filtering apparatus bodily into the balance-pan, arid partly by determining the percentage after as well as before filtration. Filters of Swedish paper were invariably used, and both the funnels and the other vessels employed were covered over as much as possible. Aqueous Solutions. a. 43-131 grammes of water took four minutes to filter, losing 0'019 gramme by evaporation. Temperature of the air 18 Cent. 99 '6 14 grammes of water took eleven minutes to filter, and lost 0*041 gramme by evaporation. Temperature, 20 Cent. At this rate, filtration of 40 to 100 grammes of a 10 per cent, solution would be tantamount to an addition of about 0-004 per cent. 1 Instead of putting the object to be weighed in the left and the weights in the right scale, in the usual way, the following method is convenient : A certain weight, greater than any likely to be used in the experiments, is put in the left scale. A 50 gramme weight will generally do. In -the right scale is placed first the empty flask, together with weights enough to produce equilibrium, and the same process repeated after the substances have been introduced. The advantage of this method is that, as the weight in the balance remains constant, the oscillations remain the same, and, by finding once for all the amount of swing corresponding to 1 milligramme, it will be easy always, when the balance is approaching equilibrium, to fix upon the proper division for the rider from observation of a single oscillation. Thus the pro- cess of weighing is facilitated. It is, however, an indispensable condition that the length of beam-arms suffer no alteration during any series of connected weighings. The substitution method (Borda's) of weighing is the only method which meets this difficulty. ESTIMATION OF PERCENTAGE COMPOSITION OF SOLUTIONS. 135 of active substance, h. Filtration, lasting for three minutes, of 50 cubic centimetres of an aqueous solution of nitrate of silver raised the proportion of the solid substance from 9*708 to 9*713 per cent. Temperature, 24*5. In this case the addition amounts to 0*005 per cent., thus agreeing with the result of the preceding experiment. Alcoholic Solutions. a. 31-007 grammes of alcohol, of 94 per cent, by weight, took four minutes to filter, and lost 0*067 gramme by evaporation. Temperature, 18 Cent. 71 '494 grammes of the same alcohol filtered in ten minutes, and lost 0*114 gramme. Temperature, 19 Cent. Had these solutions contained, to begin with, 10 per cent, of active substance, the process of filtration would have raised it to 10'022 per cent, in the first experiment, and to 10*016 per cent, in the second, b. 50 cubic centimetres of a solution of nitrate of silver in alcohol of 78 per cent, by weight took ten minutes to filter (tem- perature, 23 Cent.), and the proportion of active substance rose in one experiment from 9'686 to 9*714, and in another to 9*736, or by amounts ranging from 0*0'28 to O'OoO per cent. Assuming, therefore, that evaporation is independent of the concentration of the solutions, and, further, is proportional to the amount of filtrate (both of which postulates are only approximately true), the result of the foregoing experiments may be taken as proving that for every 10 per cent, of active substance originally present, the proportion is raised by filtration in aqueous solutions by 0*005, and in alcoholic solutions by from 0*02 to 0*05 per cent. Thus it will be seen that in the case of concentrated solutions this increase of percentage may become very considerable, and where alcohol is employed as the inactive solvent, may alter the first decimal by several units. Filtration is therefore to be avoided as far as practicable.- The degree to which errors of this kind affect the calculation of specific rotation is stated in 75. 69. Reduction of Weighings to Weight in Vacuo. If it be desired to determine with great exactness the percentage composition of the solutions, the results of the several weighings should be reduced to their values in vacuo. When pains have been taken to weigh accu- rately to milligrammes, which should, as a rule, be done, it costs but little extra trouble to apply the trifling correction reqiiisite, which is 136 PROCESS OF DETERMINING SPECIFIC ROTATION. the more desirable, as neglect of it may affect the value of the per- centage to the second place of decimals. As a rule, the error arising from non-reduction of the weights will be greater in proportion to the difference in density between the active substance itself and the solution of it employed. The effect on the specific rotation value will be greater the more concentrated the solution is, and the smaller the angle of rotation. The following simple method will suffice for the reduction: Let p be the observed weight in air of a given substance, d its specific gravity, then the weight y, by which the substance, weighed with brass weights, appears too light, owing to the pressure of the atmosphere, is given by the formula 1 y = ^.0-0012 (- - 0-12). \d I The number 0'0012 is the mean density of atmospheric air, and 0*12 is obtained by dividing unity by the specific gravity of brass, which latter may be taken as 84. The weight in mcuo P of the substance will then be 2 P = p + y. These coefficients are amply sufficient for the reduction of all weighings that occur in determining the specific rotation of active substances, and it is unnecessary to allow for changes of density in the air, so that we need not take observations of temperature and pressure at the time of weighing, 3 To facilitate calculation the following table has been prepared, giving the values of the factor 0*0012 (- - 0-12) for solutions with specific gravities ranging from 0'74 to 3'0. Putting R for this value, as in the table, the reduced weight becomes P = p + p E. 1 For the rationale of this formula see Kohlrausch, Leiffaden der praktischen Physik, 3 Aufl. S. 29. [Translated into English from the second German edition, under the title of An Introduction to Physical Measurements, by Messrs, Waller and Proctor, Churchill, London, IS 73, Svo, 12s. D.C.R.] 2 If the density of the substance exceeded 8*4, which, however, is never the case with the substances with which we have to deal, P p - y. 3 Moreover, the circumstance that the smaller weights are of platinum instead of bttiss has no appreciable effect. ESTIMATION OF PERCENTAGE COMPOSITION OF SOLUTIONS. 137 d. R. d. E. d. JR. d. . 0-74 0-00148 0-92 0-00116 1-1 0-00095 1-7 0-00056 0-76 144 0-94 113 15 90 1-8 52 0-78 140 0-96 110 2 86 1-9 49 0-80 136 0-98 108 25 82 2-0 46 0-82 132 1-00 106 3 78 2-2 40 0-84 128 1-02 103 35 74 2-4 36 0-86 125 1-04 101 4 71 2-6 32 0-88 122 1-06 099 5 66 2-8 29 0-90 119 1-08 097 6 61 3-0 26 In the calculation it will be sufficient to take the weights p to decigrammes and the specific gravity to two places of decimals. The following example of the preparation of a solution of tartrate of ethyl in wood-spirit, will show the mode of the reduction : I. Tartrate of ethyl weighed in air p = 10*898 grammes. Specific gravity of tartrate of ethyl, d = 1'2. Yalue of R for 1*2 from table = 0*00086. 10-898 or (substantially) 10'9 x 0*00086 = 0*009 Weight in vacua = 10*907 grammes. II. Weight in air of the solution in wood-spirit, p = 27*269 grammes. Specific gravity of solution, d = 0*94. Yalue of E for 0*94 from table = 0-00113. 27*269 or (substantially) 27*3 X 0*00113 = 0-031 Weight in vacuo = 27*300 grammes. The percentage composition of the solution therefore stands as follows : Uncorrected. Corrected. Difference. Tartrate of ethyl 39*965 39*952 - 0'013 Wood-spirit 60*035 60*048 + 0*013 In the process of preparing solutions there are thus two separate weighings requiring to be reduced to weight in vacuo : (1) That of the active substance, for which a knowledge of its specific weight is necessary ; and (2) that of the prepared solution, the density of which must be known at any rate for calculating the specific rotation. In 138 PROCESS OF DETERMINING SPECIFIC ROTATION. case the density of an active substance is entirely unknown, which may occur with solids, the difficulty may be got over by weighing first the solvent, whose specific gravity is known, in the flask, and then adding the active substance. The table below gives the specific gravities of a number of optically active solids and liquids, as also of several substances suitable as solvents. The specific gravities of solutions employed in polariscopic experiments seldom appear outside the limits 0'8 to 1-4. Active Substances. Oil of turpentine .. Colophonium . - '. Camphor Camphoric acid Nicotine Cholesterin Santonin , . Salicin and Phlorhizin Asparagin, crystallized Aspartic acid Mannite . . Milk-sugar Ether Alcohol Wood -spirit Acetone . . , Benzene and Toluene Acetic ether Aniline . : d. 0-85 to 0-91 85 to 1-07 0-85 to 0-99 0-85 to 1-18 0-85 to 1-01 0-85 to 1-07 0-85 to 1-25 0-85 to 1-43 0-85 to 1-50 0-85 to 1-66 0-85 to 1-52 85 to 1-54 Cane-sugar Sorbin . . Ammonium acid malate Tartaric acid . . Tartrate of ethyl . ,- : - : ' Sodium-ammonium tartrate. d. 0-85 to 1-58 0-85 to 1-65 0-85 to 1-55 0-85 to 1-75 0-85 to 1-20 0-85 to 1-59 Potassium-ammonium tartrate '85 to 1*70 Sodium-potassium tartrate. 0'85 to 1'78 Tartrate of sodium . . 0-85 to 1-79 Potassium acid tartrate . 0-85 to 1*96 Tartrate of potassium . 0.85 to 1'97 Tartar emetic 0-85 to 2-60 Inactive Solvents. 0-85 to 0-71 0-85 to 0-79 0-85 to 0-80 0-85 to 0-80 0-85 to 0-88 0-85 to 0-90 0-85 to 1-04 Acetic acid Nitro- benzene . Formic acid Ethylene chloride Carbon bisulphide Chloroform . . Carbon tetrachloride 0-85 to 1-05 0-85 to 1-20 0-85 to 1-22 0-85 to 1-26 0-85 to 1-27 0-85 to 1-48 0-85 to 1-60 D. Determination of the Specific Gravity of Liquids. 70. The only method which affords the requisite degree of exactness is that of weighing a determinate volume. For this pur- pose we may use narrow-necked pycnometers of 10 to 20 cubic centi- metres capacity, which can be filled or emptied by means of a pipette with capillary stem and india-rubber ball (Fig. 50.) The washing and drying of the apparatus is quickest done by rinsing with alcohol, followed by a little anhydrous ether. To bring the level of the liquid to the mark a roll of filter-paper or cigarette- DETERMINATION OF THE SPECIFIC GRAVITY OF LIQUIDS. 189 paper may be used. If the neck of the pycnometer have a width of about 1 millimetre, differences of from 0'5 to 2 milligrammes may be observed in the weight of the flask in successive adjustments of level, Fig. 50. at a constant temperature. The temperature is maintained constant by keeping the flask in a water-bath. Fig-. 61. Fig 52. A greater degree of exactness is attainable with SprengePs pycnometer 1 (Fig. 51). This consists of a U-shaped tube of thin glass, 1 Sprengel : Pogg* Ann. 150, 459. 140 PROCESS OF DETERMINING SPECIFIC ROTATION. the ends of which are drawn out narrow and bent at right angles. The internal diameters of these two capillary tubes a and b are made unequal ; in one, b, on which is placed a mark m t it measures about J millimetre ; in the other it is less, not exceeding J millimetre at most. The filling of the apparatus is performed by the method shown in Fig. 52, the narrow tube a being fitted by means of a small cork to the glass bulb g, to the other limb of which is attached a piece of slender india-rubber tubing. Dipping the wider tube b into the liquid and sucking at the india-rubber end, a sufficient vacuum may be produced if the bulb g be large enough, so that by keeping the tubing pinched with the finger enough liquid will enter to fill the apparatus. The operation is complete when the liquid begins to drop out at a. The bulb is then removed, and the instrument placed nearly up to the level of the ends in a water-bath of the desired temperature. In the resulting changes of volume it will be seen that it is only in the wider capillary tube b that the level of liquid oscillates that is to say, in the line of least resistance. In the narrower limb, it remains steady throughout at a. If at the desired temperature the liquid in the tube b stands outside the mark m, it can be adjusted by applying a piece of blotting-paper to the end a ; if, on the other hand, it does not reach the mark, an additional drop of the solution may readily be introduced by applying it at a on the end of a glass rod; the capillary action of the tube sufficing to absorb it and carry forward the level of the liquid within b. This operation is capable of so much exactness that in succes- sive experiments, assuming the temperature to continue perfectly uniform, the weight of the charged instrument will not vary by more than 0*1 to 0*2 milligramme. In removing the apparatus from the water- bath and wiping it previous to weighing, it is obviously requisite to avoid touching the point at a. The emptying is done by again attaching the glass bulb and blowing out the contents of the tube ; then a little alcohol and ether sucked into it will serve to rinse it out and dry it. Another form of Sprengel pycnometer is shown in Fig. 53. 1 In this a thermometer is fused into the body of the instrument, whereby the temperature of the solution can be known with absolute certainty. The apparatus is furnished with capillary tubes as in the instrument already described ; but the end of the wider tube 1 May be obtained of Dr. Geissler, Bonn ; or, Heintz, glussblower, Aachen. DETERMINATION OF THE SPECIFIC GRAVITY OF LIQUIDS. 141 Pig. 53. so is ground and fitted with a bend for immersion in the liquid to be aspirated. Moreover, both ends can be closed with ground-glass caps to pre- vent loss by evaporation. This form of pycnometer is exceedingly convenient and accurate to work with, the specific gra- vities determined from succes- sive observations not vary- ing more than two or three units in the fifth place of decimals. If the specific gravity is to be determined accurately to the fourth decimal place, neglecting variations in the fifth, the temperature of the water- bath must not be al- lowed to vary by more than 0'2 Cent. With a pycnometer of 10 cubic centimetres capa- city, filled with water at a temperature between 17 and 20 Cent., a variation of this amount will produce a differ- ence of 0*4 milligramme in the weight ; whilst in the case of other more expansible liquids the same amount of variation of temperature may cause a difference amounting to 2 milli- grammes in the weight of 10 cubic centimetres, whereby the spe- cific gravity will be altered by nearly 2 units in the fourth decimal place. In a pycnometer of 20 cubic centimetres capacity, the error will be half this amount. As in observing the angles of rotation, a normal temperature of 20 Cent, is here also to be preferred. Cylindrical glass jars of several litres capacity, so as to maintain the temperature constant for some time, may be used as water-baths. The immersed thermometer should be graduated to at least fifths of a degree. In a pycnometer of 10 to 20 cubic centimetres capacity complete uniformity of temperature is generally attained in the course of ten minutes. 142 PROCESS OF DETERMINING SPECIFIC ROTATION. 71. To determine the specific gravity or density we proceed as follows : The pycnoraeter is filled at a temperature t, first with distilled water, from which the air has been previously expelled by boiling, and afterwards with the liquid und^r examination. If now we subtract from each of these weights the weight of the instrument empty, then putting W for the weight of water, F for the weight of liquid, F ~ will represent the specific gravity of the solution at a tem- perature of t relative to that of water at the same temperature. Multiply this by the density of water at t = Q (that of water at 4 Cent, being taken as 1), we get the specific gravity of the liquid at t relative to water at 4 Cent. Lastly, taking into account the influence on the weighings of the pressure of the atmosphere (density S) we obtain the true specific weight, relative to water at 4 Cent., of the liquid at t in iricuo, which we may designate d\ from the formula 1 <*!=( -8) + 8. The value so obtained expresses the weight in grammes of 1 cubic centimetre of the liquid at t weighed in vacuo. At the normal temperature of 20 Cent, the density of water Q = 0*99826. Where some other temperature is employed the corre- sponding value of Q, can be found in the table given in 73. For the density b of air that is, the weight in grammes of 1 cubic centimetre, which varies with temperature and pressure, it will be sufficient to adopt the mean value 0'0012, or, reckoning to five places of decimals, 0-00119. If the specific gravity of the solution lies between 0'7 and 1*7, as is the case with nearly all solutions of optically active substances, the temperature of the air at the time of weighing being between 10 and 25, and the barometric pressure between 720 and 770 millimetres, the above coefficient suffices to correct the influence of atmospheric pressure accurately to within at most 4 units in the fifth place of decimals. But in calculating specific rotations, it is sufficient to know the densities to the fourth decimal place. Accordingly having ascertained the weight of the pycnometer 1 For the mode of deriving the formula, seeF. Kohlrausch, Lcitfadm d.prakt. Phys., 3 Aufl. S. 40. [The English reader may con-suit the translation already referred to on page 136. D.C.R.] DETERMINATION OF THE SPECIFIC GRAVITY OF LIQUIDS. 143 tilled to the mark at 20 Cent, first with water and then with the liquid, the annexed formula will give the specific gravity : d? = ( 0-99707) + 0-00119, log. 0-99707 = 0*998726 -*. Example : In determining the specific gravity of an aqueous solution of sugar, the pycnometer filled with water at 20 Cent, weighed W ' 13*6158 grammes, and filled with the solution F = 154015 grammes. Hence, by the formula above we get df = 1-1290. Neglecting the reduction to vacuum that is, taking the value simply F as 0-99826 we get 1*1292, making the specific gravity 0*0002 W too high. Again, an alcoholic solution of camphor gave F = 11*4260 grammes, and, as before, W = 13*6158 grammes, whence df = 0-83863. By neglecting 5 the result would be 0*83763, or 0-001 too small. Having once determined the weight of water W, contained at the normal temperature by any particular pycnometer, we may Q- 0-00119 n i c ono 0-99707\ reckon the quotient - = C (for 20 : - - J . And with this constant the specific gravity of any liquid may be found from the value F by the formula dl = F.C+ 0-00119. If, as is not unusual, 17*5 Cent, is taken for normal tempera- ture, then since at this temperature Q = 0*99875, we get d?'* = ( 0*99756) + 0-00119. Lastly, if the specific gravity of a solution has to be determined at some temperature other than that at which the weight of water contained by the pycnometer has been ascertained, the change in capacity of the apparatus that is, the coefficient of cubic expansion of glass has to be taken into account. Let F represent the observed weight of liquid in the pycnometer at the temperature t ; W the weight of water contained at temperature T ; Q the density of water at temperature T (see table 73) ; 8 the mean density of the air (0*0012) ; y the coefficient of cubic expansion of glass, which may be taken at 0-000025, 144 PROCESS OF DETERMINING SPECIFIC ROTATION: then the specific gravity of a solution at the temperature t referred to water at 4 Cent, and reduced to its value in vacua, may be obtained with sufficient accuracy from the formula E. Estimation of the Concentration of Solutions. (Preparation of Solutions in Graduated Flasks.) 72. The concentration by which term we mean the number of grammes of active substance in 100 cubic centimetres of solution can be obtained by multiplying together the density and percentage weight determined as already described. It can, however, be ascertained directly by weighing a quantity of active substance in a measured flask and forming a solution of determinate volume. The latter method will suffice in cases where the object is simply to determine the specific rotation of some particular solution of the active substance. If, on the other hand, it be desired to know the variation of specific rotation conse- quent on changes in the proportion of inactive solvent present, and so to deduce the rotation-constant of the active substance itself, as described in 24 and 25, then it is essential to know the percentage composition of the solutions. The measuring flask may indeed also serve for determining this, for which purpose all that is necessary is p io . 54 simply to take the weight also of the con- tained volume of solution. The method is somewhat simpler, requiring fewer weigh- ings than the process of preparing an inde- terminate volume of solution, and then taking the specific gravity. On the other hand, it has the disadvantage that the volume cannot be nearly so accurately known with graduated flasks as with the pycnometer, and as we have to deal with larger volumes of the solutions, it requires longer time to bring the whole to the normal temperature. Moreover, it is not so easy a matter to prepare solutions exactly of the percentage desired. For exact observations, the determination of specific gravity with the pycnometer is therefore far preferable. ESTIMATION OF THE CONCENTRATION OF SOLUTIONS. 145 The graduated flask, Fig. 54, which may have a capacity of 20 to 50 cubic centimetres, according to the size of. the polariscope- tube, should not be wider in the neck than 8 millimetres at the most, and the mark should be pretty far down, so as to avoid any want of uniformity in the solution. The solution having been prepared approximately in the flask, or in some other vessel from which it can be removed to the flask, a thermometer is inserted before finally adjusting to the mark, and the temperature br/m.ght to the standard (20 Cent.) by warming with the hand or some form of water-bath. When the temperature stands at 20/Cent. the ther- mometer should be removed, washed down with a little of the solvent employed, and the liquid then brought accurately to the mark. From the weight of the known volume of solution so prepared we have at the same time approximately the specific weight, and by applying, as iii 69, the reduction to vacuum, we may obtain a more accurate value for the percentage composition of the solution. 73. Standardising the Flasks. The volume of the graduated terms of flasks must be determined accurately in the true cubic centi- metre (the space, that is, occupied by 1 gramme of water weighed in vacuo at a temperature of 4 Cent.). If the measure is already marked, it should be filled almost to the mark with distilled water, a thermometer inserted, and the liquid warmed or cooled to the normal temperature at which the vessel is to be used (17'5 or 20 Cent.). Then withdraw- ing the thermometer, water should be added until the mark appears, to an eye looking horizontally, tangential to the concave surface of the liquid. The neck of the flask must be freed of all adhering drops, and the weight of water determined. The reduction to vacuum may then be made with sufficient accuracy, if we are using brass weights, by taking each gramme of water weighed in air as 1 milligramme too light. 1 For p grammes of water, the corrected weight P will thus be P p + 0*001^>. If now the density Q of water at the temperature of the experiment t, relative to water at 4 taken as unity, or, in other words, if the weight in grammes of 1 cubic centimetre of water at the temperature t is known, the volume in 1 Provided, that is, the weight of water does not exceed about 100 grammes. For larger quantities, the value Q'00106 gramme or 1'06 milligrammes given in ^ 69 must' bo employed. L 146 PROCESS OF DETERMINING SPECIFIC ROTATION. cubic centimetres F t contained in the measure at the temperature t is given by the equation v-L. Kt " Q The density Q of water at different temperatures is shown in the annexed table, prepared by Kosetti 1 from the results obtained by various observers (Kopp, Despretz, Hagen, Matthiessen, and Eosetti). The values are given from to 50 Cent., so as to allow the capacities of graduated flasks or pycnometers to be calculated at any of these temperatures. t. Q. t. Q. 0-99987 26 0-99687 1 0-99993 27 0-996GO 2 0-99997 28 0-99633 3 0-99999 29 0-99605 4 1-00000 30 0-99577 6 0-99999 31 0-99547 6 0-99997 32 0-99517 7 0-99993 33 0-99485 8 0-99989 34 0-99452 9 0-99982 35 0-99418 10 0-99975 36 0-99383 11 0-99966 37 0-99347 12 0-99955 38 0-99310 13 0-99943 39 0-99273 14 0-99930 40 0-99235 15 0-99916 41 0-99197 -1G 0-99900 42 0-99158 17 0-99884 43 0-99118 1S 0-99865 44 0-99078 19 0-99846 45 0-99037 .20 0-99S2 46 0-98996 21 0-9980-5 47 0-98954 22 0-99783 48 0-98910 23 0-99760 49 0-98865 24 0-99737 50 0-98819 25 0-99712 1 Rosetti: Pogg. Ann., Erg. Bel. 5, 268. ESTIMATION OF THE CONCENTRATION OF SOLUTIONS. 147 Take the case of a flask holding 25*065 grammes of water at a temperature of 20 Cent., then the weight in vacuo P = 25*065 + 0-025 = 25-09 grammes, and the capacity at 20 Cent, will be 25*69 = 25' 13 cubic centimetres. With a width of neck of 7 or 8 millimetres, there will be variations in the results of successive determinations, no matter how carefully performed, amounting to about 0*05 cubic centimetre. For example, three subsequent measurements of the above flask gave instead of 25*13 cubic centimetres, the values 25-16, 25*11, 25*17 respectively. Now a difference of O f 05 cubic centimetre has an appreciable effect on the determination of the amount of substance in 100 cubic centimetres. For instance, suppose the flask to hold 25 cubic centimetres, and to contain 5 grammes of active substance, so that the concentration c = 20 grammes, then a variation of 0*05 cubic centimetre in volume will represent a variation of 0'84 gramme in weight. The amount of error due to this source decreases the larger the flask, and the less the concentration, so that in a 50 cubic centimetre solution containing 5 grammes of active substance, or c 10, the variation only amounts to O'Ol gramme. The degree to which this error in the determination of the concentration of solu- tions affects the value of specific rotation is stated in a subsequent section ( 75). To graduate a flask for a particular volume, the corresponding weight of water is weighed into it, and the level marked upon its neck by a line. The under-surface of the concavity of the fluid-meniscus is taken as the reference level. For example, to graduate a flask to hold exactly 50 cubic centimetres at a temperature of 20 Cent., there will be required inasmuch as the previous table shows that 1 cubic centimetre of water at 20 Cent, weighs 0-99826 gramme 50 x 0*99826 = 49-913 grammes of water to give the desired volume. Again, correcting for weighing in air, this amount will be re- duced by one-thousandth, so that 49*863 grammes of water at 20 Cent, must be weighed into the previously tared flask. Since, how- ever, the volume so determined is based on a single experiment only, it is necessary, if we wish to be strictly accurate, to fill the flask several times afterwards up to the mark, and take the mean of the several weights. The result so obtained almost "invariably differs from a whole number, and since in this way the simplicity of even numbers in the calculations of concentration is lost, it 148 PROCESS OF DETERMINING SPECIFIC ROTATION. is of no importance to bestow special care on accurate drawing of the mark. "When a measure is used at some temperature t' other than that at which it has been graduated t, allowance must be made for the cubic expansion of glass, the coefficient of which may be taken as 0-000025 for 1 Cent. In calculating the volume at t', the capacity at the temperature of graduation being represented by F t , we have V v = F t [1 + 0-000025 (f - 0] where t' > t. V v = F" t [1 - 0-000025 (t - 0] wnere *' < L No account, however, need be taken of these variations in volume unless the difference of temperature is considerable and the measures of large size. 74. Mohr's 1 method of graduating measures used in titration is different. For example, in the case of a 100 cubic centimetre flask, 100 grammes of water at a temperature of 17*5 Cent, are weighed into the flask, and the resulting volume marked as 100 cubic centimetres, the reductions to volume at 4 Cent, and weight in vacuo being omitted. The cubic centimetres thus obtained are somewhat larger than the true volumes, and, as the density of water at 17'5 Cent. = 0'99875, and a deduction of 0*00105 gramme has to be made for weighing in air, the ratio between the two will be 1 : 0'9977. Hence, to reduce Mohr's cubic centimetres to their true value, they must be divided by 0*9977. If, therefore, we use Mohr's measures to deter- mine the concentration-values of solutions, the values obtained will be greater, and so the specific rotations less than when true centimetre measures are employed, and this in the above-stated proportions. Accordingly, concentrations estimated in Mohr's cubic centimetres should be multiplied by 0'9977, and specific rotations calculated there- from should be divided by 0'9977, to bring them to their proper values for true centimetres. The definition of specific rotation presupposes the use of the true centimetre, and upon this supposition all scientific data thereto relating are based. 1 Mohr : Lehrbuch der Titrlrmethode, 4 Aufl. S. 37. INFLUENCE OF ERRORS OF OBSERVATION. 149 F. Influence of the several Observation- Errors on Specific Rotation Values. 75. All the factors entering into the formula [a] = -^ - or j , are severally subject to observation-errors, the eifects of which JLj may be estimated as below : 1. As regards the angle of rotation a, the experiments given in 60 show that the values obtained by different observers with different instruments do not in general vary by more than the hundredth part of a degree, and that the mean error for a single observation may be taken as + 0*025. In the calculations following a maximum error of 0'05 has been allowed. 2. The length L of the tubes can easily be determined by the method described in 66, so that the variation in a length of 100 millimetres never exceeds 0*05 millimetre. 3. The specific gravity d of solutions can be found accurately to four places of decimals by means of the pycnometer (see 70 and 71). The maximum error here, which may occur when the normal tempera- ture has been taken more than 1 wrong, or, in particular cases, when the correction in vacuo has been omitted, may be taken as O'OOl. 4. As regards the percentage composition^ of solutions, neglect to reduce the weighings may involve an error of about 0*01. In cases, however, where filtering is necessary (see 68), the percentage may be increased by evaporation to the amount of 0' 00 5 in aqueous solutions, and 0'02 to 0*05 in alcoholic solutions for each 10 per cent, of active substance. In choosing a value as nearly as possible appli- cable to all liquids, 0'02 has been allowed in what follows as error under this heading. 5. In determining the concentration c (see 73), an error of 0*04 gramme may occur in solutions containing 20 grammes of active substance. This amount has been taken as a mean. In order approximately to estimate the actual influence of these errors individually on the value obtained for specific rotation, the following examples have been tabulated for substances having unequal rotatorv powers in solutions of different degrees of con- centration. 150 PROCESS OF DETERMINING SPECIFIC ROTATION. I. Solutions of Oil of Turpentine in Alcohol. Error. a. L. d. P- c. M- Diff. 50 per cent. Solution. 15-49 100 0-825 49-97 41-23 37-57 a = 0-05 15-54 100. 0-825 49-97 37-70 0-13 L = 0-05 15-49 100-05 0-825 49-97 37-55 0-02 d = 0-001 15-49 100 0-826 49-97 37-53 0-04 p = 0-02 15-49 100 0-825 49-99 37-56 o-or c = 0-04 15-49 100 41-27 37-53 0-04 30 per cent. Solution. 9-23 100 0-813 29-97 24-37 37-88 a = 0-05 9-28 100 0-813 29-97 38-09 0-21 L = 0-05 9-23 100-05 0-813 29-97 37-86 0-02 d = 0-001 9-23 100 0-814 29-97 37-83 0-05 p = 0-02 9-23 100 0-813 29-99 37-85 0-03 c = 0-04 9-23 100 24-41 37-81 0-07 10 per cent. Solution. 3-09 100 0-801 10-01 8-02 38-54 a = 0-05 3-14 100 0-801 10-01 39-16 0-62 L = 0-05 3-09 100-05 0-801 10-01 38-52 0-02 d = 0-001 3-09 100 0-802 10-01 38-49 0-05 p = 0-02 3-09 100 0-801 10-03 38-46 0-08 c = 0-04 3-09 100 ' 8-06 38-34 0-20 INFLUENCE OF ERRORS OF OBSERVATION. 151 II. Solutions of Cane-Sugar in Water. Error. a. L. d. P- c. [4 Diff. 40 per cent. Solution. 31-17 100 1-177 39-98 47-06 66-24 a = 0-05 31-22 100 1-177 39-98 66-35 o-ir L = 0-05 31-17 100-05 1-177 39-98 66-21 0-03 d = 0-001 31-17 100 1-178- 39-98 66-18 0-06 p = 0-02 31-17 100 1-177 40-00 66-21 0-03 c = 0-04 31-17 100 47-10 66-18 0-06 17 per cent. Solution. ' 12-06 100 1-068 16-99 18-15 66-46 a = 0-05 12-11 100 1-068 16-99 66-74 0-28 Z= 0-05 12-06 100-05 1-068 16-99 66-43 0-03 d = 0-001 12-06 100 1-069 16-99 66-40 0-06 p = 0-02 12-06 100 1-068 17-01 66-39 0-07 c = 0-04 12'06 100 18-19 66-30 0-16 5 per cent. Solution. 3-39 100 1-018 5-00 5-09 66-60 __ a = 0-05 3-44 100 1-018 5-00 67-58 0-98 Z= 0-05 3-39 100-05 1-018 5-00 66-57 0-03 d - 0-001 3-39 100 1-019 5-00 66-54 0-06 p = 0-02 3-39 100 1-018 5-02 66-54 0-26 c = 0-04 3-39 100 5-13 66-08 0-52 152 PROCESS OF DETERMINING SPECIFIC ROTATION. III. Solutions 9f Nicotine in Akthtl. Errr. Z. * * c. [] Diff. 60 per cent. Solution. 83'69 100 0-920 59-93 55-14 151-79 . = 0-05 83-74 100 0-920 59-93 151-88 0-09 L= 0-05 83-69 100-05 0'920 59-93 151-71 0-08 d = 0-001 83-69 100 0-921 59-93 151-62 0-17 p = 0'02 83-69 100 0-920 59-95 151-74 0-05 e = 0-04 83-69 100 55-18 151-67 0-12 30 per cent. Solution. 37'35 100 0-856 30-03 25-68 145-47 a = 0-05 37-40 100 0-855 30-03 145-66 Z = 0-05 37-35 100-05 0-855 30-03 M5-39 d = O'OOl 37-35 100 0-856 30-03 145-30 p - 0-02 37-35 100 0-855 30-05 145-37 e = 0-04 37-35 100 25-72 145-22 15 per cent. Solution. 17.470 100 0-825 14-96 12-34 141-55 a = 0-05 17-52 100 0-825 14-96 141-96 L= 0-05 17'47 100-05 0-825 14-96 141-48 d = 0-001 17-47 100 0-826 14-96 141-38 p = 0-02 ' I7 . 47 o 100 0-825 14-98 141-36 c - 0-04 17-47 100 12-38 141-11 INFLUENCE OF ERRORS OF OBSERVATION. 153 According to the foregoing examples, then, it is the angle of rotation above all that one needs to determine with the utmost accuracy, and the more so the less the angle is. The error in the measurement of tube length influences the result but slightly, that in the determination of specific gravity rather more, the effects of both being greater the higher the specific rotation. As regards the error in determining percentage composition and concentration of solutions, this of course exerts a greater effect the more dilute the solutions. In practice, however, the amount is not so great as shown in the foregoing calculations, because the amount of error in determining concentration and percentage composition is there assumed to be the same for all solutions, whereas it diminishes with increased dilution. In general, indeed, the errors are seldom so large as they are assumed to be in the foregoing examples, and the smaller they can be made the less of course will the result obtained differ from the true value. Besides, errors made by any single observer may be partly positive and partly negative, and so become eliminated from the result. In any case it will be seen that careful working is requisite to get even the first place of decimals correct, and that in all researches of this kind it is necessary to know the degree of accuracy with which the several measurements have been made before any judgment can be formed on the value of the final result. vi: PRACTICAL APPLICATIONS OF ROTATORY POWER. A. Determination of Cane-Sugar. OPTICAL SACCHARIMETRY. 76. The determination of the percentage of sugar in aqueous solutions is based upon the following propositions established by Biot: 1. The amount of deviation of the plane of polarization is proportional to the length of the liquid column. 2. The deviation is proportional to the concentration that is, to the number of grammes of sugar in the unit-volume (100 or 1,000 cubic centimetres) of solution. Accordingly, by determining once for all the angle of rotation given by a single saccharine solution of known concentration in a tube of a certain length, we are able by simple proportion to calcu- late the number of grammes of sugar in 100 cubic centimetres of any solution of unknown strength from its observed angle of rotation. As before explained, 23 and 37, Biot's second proposition is not strictly correct, inasmuch as the specific rotation of cane-sugar decreases somewhat with increase of concentration, so that a solution of double percentage does not give exactly double the angle of rotation, but rather less. The errors from this source are, however, small, and apart from very accurate experiments may be entirely neglected. In the following account of the saccharimeters, the pro- position is at first taken as strictly true ; corrections for varying rotation being always discussed separately. It is evident that any of the forms of polariscope already described DETERMINATION OF CANE-SUGAR. 155 will serve as a saccharimeter, if the graduated arc be replaced by a scale on which the corresponding sugar percentages can be read oft directly. Instruments, however, on a different optical principle have been constructed expressly for determining solutions of sugar. Of these so-called saccharimeters, now so extensively used in trade, the most important are the following : ' (a.) The Sokil-Ventzke-Scheibler Saccharimeter. 77. This very ingenious instrument was originally devised in the year 1848, by the Paris optician Soleil, 1 and more recently improved by Soleil and Duboscq. 2 In Germany, various alterations were made in the instrument by Yentzke, 3 who introduced a different scale, and also by Scheibler, 4 who devised important improvements in the mechanical arrangements. The optical principle of the instrument is based upon the following facts discovered by Biot : 1. That when a polarized ray is transmitted through several media possessing rotatory power in different directions, their separate activities may become either partially or wholly neutralized, according to the lengths of the media. 2. That the rotatory dispersion of cane-sugar is the same as that of quartz. White day or lamp-light is used with the ' instru- ment. The optical parts are as shown in Fig. 55, the course of the Fig. 55. n o f e G light being from right to left. Starting from the right-hand side, we have : A. The so-called regulator for restoring the sensitive tint, con- sisting of a rotating Nicol's prism , and a plate of quartz 1 Soleil : Comptes Rend., 24, 973 ; 26, 162. 2 Soleil and Duboscq : Idem. 31, 248. 3 Ventzke: Erdm., Jottrn.fiir prakt. Chem. 25, 84; 28, 111. 4 Scheibler: Zeitsch. des Vereins fur Rubenzuckerindustrie, 1870, 609. 156 PRACTICAL APPLICATIONS OF ROTATORY POWER. b (dextro-rotatory or Isevo-rotatory), groimd perpendicu- larly to the axis. B. The polarizer, for which an achromatized calc-spar prism, a Se'narmont's prism, or double quartz prism can be used. It is arranged with its principal section vertical. The polar- ized extraordinary ray is allowed to proceed along the axis, but the sidewards-refracted ordinary ray is intercepted by a diaphragm. The face of the prism towards A is ground convex, so that light may emerge approximately parallel. C. The bi-quartz, composed of two plates, the one of dextro- rotatory, the other of Iscvo-rotatory quartz, fitted accurately together. They may be either 3'75 millimetres or 7*5 millimetres thick, and are fixed in a brass case, so that the line of junction remains vertical. (A front view is shown above C.) D. The experimental tube. E. The so-called rotation- compensator. This consists of a plate of quartz c, which may be dextro-rotatory, in which case the other two plates, d, must be made of laovo-rotatory quartz. The latter are ground to a wedge shape, and are made to slide over one another, so that their combined thickness may be made either equal to that of c, or greater or less, the distance moved to effect any particular adjustment being shown by an attached scale. The plate c may be made of left-handed quartz, but in that case the wedges must be right-handed. F. The analyzer ', which may consist of an achromatized calc-spar prism. Its principal section must be arranged parallel to that of the polarizer B, in case the thickness of the bi-quartz of the instrument, C, is 3*75 millimetres, and perpendicular thereto when the thickness is 7*5 millimetres. G. A small Galilean telescope, consisting of objective e and eye- piece /. The latter is to be adjusted so that the line of junction of the plates of the bi-quartz C is sharply defined 78. In order clearly to understand the action of the several parts, let us suppose first that we are merely dealing with the polarizer B and analyzer F, and that these are arranged with prin- cipal sections parallel, and the field at its maximum of illumination. Let the active bi-quartz C be now introduced between .Z? and F] the DETERMINATION OF CANE-SUGAR. 157 white light coming from B will thus be rotated, and suffer decom- position into its component coloured rays. Now of the emergent rays, those whose plane of polarization is at right angles to that of the analyzer will not be transmitted ; and should these be the yellow rays, the remainder will, in transmission, combine to a pale lilac mixed tint which, with the slightest alteration of the plane of polar- ization, passes either into pure red or pure blue. This intermediate colour has been already referred to in 47 as the sensitive or transition tint. With the polarizer and analyzer undisturbed in their parallel position, the sensitive tint will appear when the bi- quartz C has the thickness requisite to rotate the yellow rays exactly 90 to the right or left. This requires a thickness of 3'75 millimetres, since, according to Biot, a thickness of 1 millimetre of quartz rotates mean yellow rays through an angle of 24, whence we get the proportion, 24 : 1 = 90 : 3 '75. If, on the other hand, the corresponding planes of polarizer and analyzer were set at right angles to each other, a rotation through 180 would be required to eliminate the yellow rays, and the bi-quartz must then have a thickness of 7*5 millimetres. In one half of the bi-quartz the sensitive tint is produced by dextro- rotation, in the other by Ia3vo- rotation, and as the thickness of the two sides is equal, the tints produced will be the same. Let the compensator E now be put in its place, the quartz wedges being so adjusted that their combined thickness is exactly equal to that of the quartz plate c. As the rotatory powers of c and d act in opposite directions, they neutralize each other, and the sensitive tint still occupies the field of vision. This position of the wedges corresponds with the zero-point of the scale. If, however, we shift the relative position of the wedges, the transmitted coloured rays will suffer rotation, and the analyzer will eliminate those of which the planes of polarization are perpendicular to its own. The other rays which pass on combine to produce a new chromatic mixture, which will, necessarily, be unlike for the rays transmitted by the respective halves of the bi-quartz (7. Thus, if the compensator be so adjusted that its action is dextro- gyrate, the rays contributed by the dextro- rotatory half of the bi-quartz will undergo an increase, and those coming from the Isevo-rotatory half a decrease, in the amount of their rotation. Seen through the analyzer, the two halves will thus appear differently coloured green and blue predominating in one, red and orange light in the other ; and these tints will change places when the action of the compensator is lacvo-gyrate. 158 PRACTICAL APPLICATIONS OF ROTATORY POWER. Lastly, having again set the compensator to zero and repro- duced the. sensitive tint, let a tube filled with an optically- active solution be introduced. A splitting of the field of vision into two different coloured halves will once more occur. -By sliding the quartz wedges, d, so as to produce rotation opposite to that of the solution, a position may be found where the action of the latter is annulled, and this will be indicated when the halves of the field of vision again exhibit uniformly the sensitive tint. The rotatory power of the substance introduced can thus be measured by the amount of change in the combined thickness of the quartz wedges, d, as indicated by the amount of adjustment required to bring into view the sensitive tint. For the proper action of the compensator, it is, however, requi- site that the active solution should have the same dispersive power as quartz, otherwise the effects of dispersion due to the solution will not be exactly neutralized by the opposite dispersion of the quartz. As before stated, 18, this is the case with cane-sugar ; but there are many substances which do not fulfil this condition, as, for instance, cholesterin, and in such cases, at least with strong rotations, the compensator can no longer be adjusted so as to restore a perfectly uniform colour to the field of vision. "With Soleil's instrument, exact data are therefore only attainable in the case of substances whose rotatory dispersion does not materially differ from that of quartz. The sensitive tint makes its appearance as above described when ordinary white light is used. When, on the contrary, lamp-light is employed, which contains the coloured rays in somewhat different proportions, there appears instead not th blue-violet, but a red- dish tint, and a similar alteration may occur when the active solution is itself coloured. In this way arises the need for yet another addition to the instrument, namely, the regulatpr A, by which we can still produce the sensitive tint. It consists of a rotating Nicol prism, a, and a quartz plate, b, both placed in front of the polarizer B. When light which has been polarized by the Nicol falls on the quartz plate, it undergoes rotatory dispersion, and according to the position of the Nicol in reference to the polarizer, B, so will certain rays suffer total -extinction by the polarizer or be transmitted by it with diminished intensity. In this way we are able to weaken the red and yellow rays of lamp-light, and so admit to the bi-quartz, C, a selected mixture of rays, which, in consequence of the rotation there experienced, reproduces the sensitive tint. As DETERMINATION OF CANE-SUGATl. 159 the polarizer, B, brings the transmitted rays into one plane of polarization, the two halves of the bi-quartz will appear coloured alike, the tint being variable at will by turning the Nicol a. A similar process is adopted in dealing with coloured solutions. The colour of the latter should, however, never be more than faint, otherwise too much light will be lost by absorption. The two portions forming the regulator can be placed at the eye-end instead of the light-end if preferred, as is done in instru- ments of French make. 79. The external form of SoleiPs saccharimeter with Scheibler's improvements is shown in Fig. 56, which represents the instrument as supplied by Berlin opticians. 1 On a brass stand rests, with horizontally rotating motion, a blackened metal trough, h h y in which the experimental tube It is Fig. 56. laid, the upper half of the trough serving as a cover, which can be shut down during observations so as to exclude extraneous light. The end of the trough next the light in the Fig. the right-hand end is connected with a brass tube enclosing at one end the bi-quartz Z>, at the other the polarizer C. Into this tube fits the rotatory tube, A B, containing the. regulator with its Nicol at A, and the quartz plate at B. The rotation of the tube is effected by wheel and pinion movement, worked by means of a rod with the milled-head L. The ocular part of the instrument contains at G the quartz plate of the compensator, and at E F the. two quartz wedges. Each of the wedges is cemented to a similar wedge of glass, so as to form 1 May be obtained of Schmidt and Hacnsch, Stallschreiberstrassc 4, Berlin ; Dr. Steeg and Reuter, Homburg v. d. Hohe. 160 PRACTICAL APPLICATIONS OF ROTATORY POWER. two piano-parallel plates, which are set in brass frames. One of these plates is fixed, while the other has a horizontal sliding motion, for which purpose it is provided at the bottom with a side to side rack and pinion motion, worked by the milled-head M. The frame on the upper edge of the movable plate carries the divided scale, and that of the fixed plate a vernier. For reading the latter an inclined mirror s throws the image of the scale along the axis of the tube, which is fitted with a lens K. The piece, H 7, contains the analyzer and the telescopic lenses, the eye-glass being movable. At H in the Fig. is shown a screw-head, which admits of the ana- lyzer being adjusted to its proper position in relation to the fixed polarizer. It is only to be used, however, either by the makers in the first adjustment of the instrument, or when it has got out of proper adjustment when, that is, we cannot by any movement of the quartz wedges bring a uniform tint into the two halves of the field. When this is the case, either the polarizer or analyzer must have been disturbed. To readjust the instrument, the two quartz wedges along with the fixed plate are removed, and the screw H turned until uniformity of tint in the field is attained. To fix the zero-point, another screw, not shown in the Fig., is attached to the quartz wedge frame which carries the scale, and allows of a certain amount of the adjustment of the latter. Lastly, as regards the length of the solution tubes, the instrument is generally arranged for tubes 2 decimetres in length ; but saccharimeters capable of taking 4 and 6 decimetre tubes are made, and are of service in the analysis of weak saccharine solutions. 80. In using the saccharimeter, it is set up against a gas or paraffin lamp furnished with a metal chimney having a side opening (see Fig. 25, p. 102), care being taken to keep it a distance of at least 5 centimetres (2 inches) from the flame, to prevent the Nicol becom- ing heated. The manipulation is then as follows : 1. A tube, either empty or filled with water, is laid in the instrument, and the eye-piece of the telescope drawn out until the vertical joining line bisecting the circular bi-quartz appears sharply denned ; next taking the milled-head M (Fig. 56), the movable quartz wedge must be adjusted, until over both halves of the field an approximately uniform colour prevails. 2. The regulator is then moved by means of the milled-head L of the side gearing, so as to bring 1 into view that sensitive tint DETERMINATION OF CANE-SUGAR. 161 \V hich with the slightest displacement backwards or forwards of the movable quartz wedge produces the most distinct colour- differentiation in the two semi-circles. Thus it will be found that if we start with a uniform deep-red or deep-blue tint, the quartz wedge has to be moved much further before we can distinctly recognize a difference of colour in the halves, than if we had started from a uniform bright violet tint. For most eyes the best position of the regulator is that which gives a sensitive tint most nearly approaching to white. Here a very slight movement of the quartz wedge will cause one half to exhibit a faint greenish tinge, and the other a flesh-pink, which on further turning of the milled -head, M, passes into green and orange-red respectively. In arranging the regulator for this position we do not get exactly the ordinary sensitive tint the reddish-purple, which denotes most perfect extinction of the yellow light. Some of the yellow rays are allowed to pass, thereby making possible the green and orange colours which appear. It is, however, in other respects immaterial which tint is chosen for purposes of observation. 3. Having once decided upon the sensitive tint, the quartz wedge is adjusted to give the greatest possible similarity of colour in the halves of the field and the corresponding reading on the scale noted. This should be several times repeated, the mean of the readings being taken as the zero-point of the instrument. Should this not coincide with the zero- point of the scale, the latter must be adjusted, by slightly moving the screw referred to in 79 as being fixed on the brass frame of. the wedge. The position of the zero-point must be verified from time to time. Moreover, it is found to vary con- siderably for different eyes. 4. If the tube be now filled with a solution of cane-sugar and laid in its place, colour-dissociation at once takes place, and may be made to vanish again by moving the quartz wedge in such a way that the 100 point on the scale is made to approach the zero-point of the fixed vernier. If the solution be perfectly colourless, the screw L, Fig. 56, which manipulates the regulator, need not be touched ; but if, on the contrary, as frequently happens, it has a yellowish tinge, we must disturb the screw a little to the right or left, until we obtain, as nearly as possible, the tint used in fixing the zero-point. By making several such adjustments of the quartz wedge to the position in which colour- uniformity is shown, we arrive at an accurate determination of the rotation. With a little practice; it will be found easy to get observa- M 162 PRACTICAL APPLICATIONS OF ROTATORY POWER. tions not varying from one another by more than - 4 division of the -scale at the most, provided that the instrument is well constructed. Where greater differences occur, as will be the case with coloured solutions, the number of observations must be increased. As a rule, five are enough to determine the mean value within + O'l of a division. This instrument is, of course, unsuited for the colour-blind. 81. The graduation of the saccharimcter scale, according to Ventzke, is made by laying in the instrument a tube 2 decimetres long, filled with an aqueous solution of pure sugar, having at the temperature of 17'5 Cent, a specific gravity of I'l, and marking the point of the observed deviation as 100. A solution of the above density contains in 100 cubic centimetres exactly 26'048 grammes of sugar, so that it can be more easily prepared by weighing this quan- tity and adding the proper amount of water. The space between the 100 point and the zero-point is then divided into one hundred equal parts, and the graduation extended some way (30 or 40 divisions) on the other side of the zero-point. As cane-sugar is dextro-rotatory, the latter divisions of the scale will indicate la>vo-rotation, and must be marked with the negative sign. Assuming that deviation is exactly proportional to concentration, each division of Ventzke's scale will indicate a sugar value of 0'26048 gramme in 100 cubic centimetres of solution (or 2 '6048 grammes per litre). Accordingly the process for estimating a saccharine solu- tion is as follows : To determine concentration (the number of grammes of sugar in 100 cubic centimetres of solution), we fill a 2 decimetre tube with the solution, note the deviation on the scale, and multiply the number of degrees by 0-26048. The solution must not, 'of course, contain more than 26*048 grammes of sugar in 100 cubic centimetres, otherwise the indication on the scale would pass out- side the 100 point. To determine per cent, composition (the number of grammes of sugar in 100 grammes of solution), weigh out 26*048 grammes of the solu- tion, dilute to the mark in a 100 cubic centimetre flask, with this latter solution fill a 2 decimetre tube, and note the degree of devia- tion on the scale. This will indicate directly the percentage of sugar in the original solution. The analysis of solid saccharines may be effected similarly : To DETERMINATION OF CANE-SUGAR. 163 estimate the value of a crude sugar, for instance, 26'048 grammes of substance are dissolved in water, diluted to 100 cubic centimetres, and observed in a 2 decimetre tube. The degree of deviation expresses directly the percentage of pure sugar in the substance. If instead of 26*048 grammes we had used some other weight P of liquid, or solid saccharine matter, in preparing the 100 cubic cen- timetre solution, then, taking the degree of deviation observed in a 2 decimetre tube as a, the percentage composition will be 26-048 xa * = --JT- Moreover, the percentage weight of a sugar solution can be calcu- lated from the concentration as determined directly, provided we know the specific gravity that is, the weight of 100 cubic centi- metres. When a tube 1 decimetre in length is used instead of a 2 deci- metre tube, the scale-readings must, of course, be doubled ; similarly, in using a 4 decimetre tube, they must be halved. For the method of preparing sugar solutions for the sacchari- mcter, see 92. The original method as used by Ventzke was to prepare, by means of an areometer, a solution of the saccharine substance to be analyzed of a specific gravity 1*1, and to examine this in a 2 decimetre tube. The observed deviation was then taken as giving directly the weight per cent, of sugar in dry substance. This method, however, w r hich was intended to dispense with all weighings, does not yield accurate results, as the salts contained in natural sugars always have a specific gravity different from that of the sugar itself. It has therefore been abandoned, but the awkward normal weight of 26 '048 grammes con- tinues in use. It would be much more convenient to substitute some simpler figure as, for example, 20 grammes in which case, how- ever, a re-calculation of the tables prepared for Ventzke's instrument would be necessary. 82. Correction of Saccharimeter- Readings for slight D pro- portionality between Rotation and Concentration. As shown by the researches of Schmitz and Tollens, already described 37, the specific rotation of sugar is not constant for solutions of different concentra- tions, but increases inversely as the concentration. Thus, given that a solution containing 26*048 grammes of sugar in 100 cubic centimetres records 100 on the scale of the saccharimeter, the reading M 2 164 PRACTICAL APPLICATIONS OF ROTATORY POWER. 50 on the same scale will not be recorded exactly by one containing 13'024 grammes, but by a solution containing a somewhat smaller sugar percentage. Hence the need, at least in the case of exact observations, of correcting the saccharins etric readings. Schmitz 1 has calculated the required correction, on the basis of the following observations : No. of Concentra- M [ID " Solution. tion c. Observed. Calculated. Difference. I. 27-6407 66-328 66-308 - 0-020 II. 18-1751 66-375 65-388 + 0-013 III. 10-3994 66-460 66-453 - 0-007 IV. 5-0955 66-495 66-498 !; + 0-003 According to these experiments the increase of specific rotation with decrease of concentration may be expressed by the following interpolation-formula, from which the calculated values in the table were obtained : [o] D = 66-541 - 0-0084153 c. Putting [a] n as the specific rotation calculated from this formula, for a normal solution containing 26'048 grammes of sugar in 100 cubic centimetres of solution, and [a] c as that for some other solution of lower concentration c, then |r j represents the proportion in which the L a Jn concentration and per cent, composition will appear too high when estimated on the supposition that the rotation varies uniformly there- with. To obtain the true values the results must, therefore, be divided by the above fraction. This calculation is exemplified in detail in the table annexed. Col. 1. JV gives the scale-reading at every ten divisions. ,, 2. c, the number of grammes of sugar in 100 cubic centimetres of solution, assumed to correspond. ,, 3. [o] N and [a] c , the specific rotation of sugar for the above -mentioned concentra- tions (26-048 and c}, calculated from the interpolation -formula. We ,, 4. -.- -. = Q, the ratio of the specific rotations. 1 Schmitz: Zeitsch. des Vereinsfur Riibenzuckerindustrie, 1878,63. DETERMINATION OF CANE-SUGAR. 165 L 5 __, the corrected number of grammes of sugar in 100 cubic centimetres of solution. n 6. c , the difference between the assumed and corrected values of the concentration. ,, 7. ~ or - , the corrected scale -reading. Q, 26'048 Q ,, 8. N~ -^ the difference between the corrected and un corrected percentages. 1. 2. 3. 4. 5. 6. 7. 8. [01 c c V N N c M L"*J Q [] Q N ~~Q m 26-048 [a] n = 66-322 I -00000 26-048 o-ooo 100 o-ooo 90 23-443 , . [a] e = 66-344 1-00035 23-435 0-008 89-969 0-031 80 20-838 66-366 1-00070 20-824 0-014 79-945 0-055 70 18-234 66-388 1-00101 18-216 0-018 69-930 0-070 60 15-629 ,, 66-409 1-00132 15-608 0-021 59-920 0-080 50 13-024 66-431 1-00165 13-003 0-021 49-917 0-083 40 10-419 66-453 1-00198 10-398 0-021 39-921 0-079 30 7-814 66-475 1-00232 7-796 0-018 29-930 0-070 20 5-210 ,, 66-497 1-00265 5-196 0-014 19-947 0-053 10 2-605 ,, 66-519 1-00297 2-597 0-008 9-970 0-030 As the and 100 marks of the saccharimeter scale, indica- ting gramme and 26*048 grammes concentration respectively, are given as fixed, the difference between the corrected and the unconnected readings will be greater the further their distance from these points, and greatest midway between them. This is shown in cols. 6 and 8. The fact that the formula above given for the calculation of specific rotation refers to ray D, whereas observations with the Soleil- Scheibler saccharimeter are taken with the transition tint, has no effect upon the results, the ratio jik being the same for all rays. The differences between the corrected and uncorrected values are thus seen to be not inconsiderable for solutions of medium con- centration. The corrections required have been calculated by Schmitz for each degree of the saccharimeter scale and embodied in the accompanying table : 166 PRACTICAL APPLICATIONS OF ROTATORY POWER. Degrees of Saccharimeter Scale. Corrected per cent. Grammes of Sugar in 100 cub. cent. Solution. Uncorrected. Corrected. Difference. 1 1-00 0-261 0-260 o-ooi 2 1-99 0-521 0-519 0-002 3 2-99 0-781 0-779 0-002 4 3-99 1-042 1-039 0-003 5 4-98 1-302 1-298 0-004 6 5-98 1-563 1-558 0-005 7 6-98 1-823 1-817 0-006 8 7-98 2-084 2-078 0-006 9 8-97 2-344 2-337 0-007 10 9-97 . 2-605 2-597 0-008 11 10-97 2-865 2-857 0-008 12 11-97 3-126 3-117 0-009 13 12-96 3-386 3-376 o-oio 14 13-96 3-647 3-637 o-oio 15 14-96 3-907 3-896 0-011 16 15-96 4-168 4-156 0-012 17 16-95 4-428 4-416 0-012 18 17-95 4-689 4-676 0-013 19 18-95 4-949 ^4-936 0-013 20 19-95 5-210 5-196 0-014 21 20-95 5-470 5-456 0-014 22 21-94 5-731 5-716 0-015 23 22-94 5-991 5-976 0-015 24 23-94 6-252 6-236 0-016 25 24-94 6-512 6-496 0-016 26 25-94 6-773 6-756 0-017 27 26-94 7-033 7-016 0-017 28 27-93 7-293 7-276 0-017 29 28-93 7-554 7*536 0-018 30 29-93 7-814 7-796 0-018 31 30-93 8-075 8-056 0-019 32 31-93 8-335 8-316 0-019 33 32-93 8-596 8-577 0-019 34 33-93 8-856 8-837 0-019 35 34-92 9-117 9-097 0-020 36 35-92 9-377 9-357 0-020 37 36-92 9-638 9-618 0-020 DETERMINATION OF CANE-SUGAK. 167 Degrees of Saccharimeter Scale. Corrected per cent. Grammes of Sugar in 100 cub. cent. Solution. Uncorrected. Corrected. Difference. 38 37-92 9-898 9-878 0-020 39 38-92 10-159 10-138 0-021 40 39-92 10-419 10-398 0-021 41 40-92 10-680 10-659 0-021 42 41-92 10-940 10-919 0-021 43 42-92 11-201 11-180 0-021 44 43-92 11-461 11-440 0-021 45 44-92 11-722 11-701 0-021 46 45-92 11-982 11-961 0-021 47 46-92 12-243 12-222 0-021 48 47-92 12-503 12-482 0-021 49 48-92 12-764 12-743 0-021 50 49-92 13-024 13-003 0-021 51 50-92 13-285 13-264 0-021 52 51-92 13-545 13-524 0-021 53 52-92 13-805 13-784 0-021 54 53-92 14-066 14-044 0-022 55 54-92 14-326 14-305 0-021 56 55-92 14-587 14-566 0-021 57 56-92 14-847 14-826 0-021 58 57-92 15-108 15-087 0-021 59 58-92 15-368 15-347 0-021 60 59-92 15-629 15-608 0-021 61 60-92 15-889 15-868 ^^ 0-021 62 61-92 16-150 16-130 0-020 63 62-92 16-410 16-390 0-020 64 63-92 16-671 16-651 0-020 65 64-92 16-931 16-912 0-019 66 65-93 17-192 17-173 0-019 67 66-93 17-452 17-433 0-019 68 67-93 17-713 17-694 0-019 69 68-93 17-973 17-954 0-019 70 69-93 18-234 18-216 0-018 71 70-93 18-494 18-476 0-018 72 71-93 18-755 18-738 0-017 73 72-93 19-015 18-998 0-017 74 73-94 19-276 19-259 0-017 168 PRACTICAL APPLICATIONS OF ROTATORY POWER. Degrees of Saccharimeter Scale. Corrected per cent. Grammes of Sugar in 100 cub. cent. Solution. Uncorrected. Corrected. Difference. 75 74'-94 19-536 19-519 0-017 76 75-94 19-797 19-781 0-016 77 76-94 20-057 20-042 0-015 78 77-94 20-317 20-302 0-015 79 78-94 20-578 20-564 0-014 80 79-95 20-838 20-824 0-014 81 80-95 21-099 21-085 0-014 82 81-95 21-359 21-346 0-013 83 82-95 21-620 21-608 0-012 84 83-95 21-880 21-868 0-012 85 84-96 22 141 22-130 0-011 86 85-96 22-401 22-391 o-oio 87 86-96 22-662 22-652 o-oio 88 87-96 22 922 22-912 o-oio "89 88-97 23-183 23-174 0-009 90 89-97 23-443 23-435 0-008 91 90-97 23-704 23-696 0-008 92 91-98 23-964 23-957 0-007 93 92-98 24-225 24-219 0-006 94 93-98 24-485 24-480 0-005 95 94-98 24-746 24-742 0-004 96 95-98 25-006 25-002 0-004 97 96-99 25-267 25-265 0-002 98 J^k 97-99 25-527 25-525 0-002 99 A 98-99 25-78S 25-787 . . o-ooi 100 JPioo-oo 26-048 26-048 o-ooo As will be seen by comparing cols. 1 and 2, the corrected per- centages at points between 17 and 84 on the scale, differ from the actual readings by amounts ranging from 0'05 to 0*08. Within these limits, therefore, and reckoning percentages to tenths only, it will suffice to deduct 0*1 per cent, from the actual readings. With rota- tions of less than 16 or more than 85 scale degrees, such as occur in the analysis of natural sugars and their refined products, the correc- tion is superfluous. DETERMINATION OF CANE-SUGAR. 169 83. To convert the degrees on Ventzke's scale into true rotation- degrees, as is necessary when the specific rotation of a substance is to be determined with this instrument, the formula [a] D = 66'541 0-0084153 c, given in 82, can be used. With concentration c = 26*048, [a] D = 66*322, and determining the angle of rotation given by such solution, in a tube 2 decimetres long, from the equation . a x 1Q i- = 66*322 we get oFiT=^34-55. That is to say, a / X /wO*U4o solution of 26*048 grammes of sugar in 100 cubic centimetres, which rotates mean yellow ray / to the amount of 100 divisions on the Ventzke scale, would record on instruments having angular gradua- tion a rotation of the sodium ray D through an angle of 34*^5 d . Hence, 1 Ventzke's scale (ray/) = 0*3455 angular measurement (ray D). And further assuming the dispersive power of the substance to be equal to that of quartz, in which, as we have seen ( 18), the rota- tions for rays D and/ are to one another as 1 to 1*1306, we obtain : 1 Ventzke's scale (ray/) = 0*3906 angular measurement (ray/). Another mode of arriving at these relations is afforded by the observed fact (see 18) that a quartz plate 1 millimetre thick rotates ray D through 21*67 and ray/ through 24*5 angular measure. In a subsequent table ( 91) the angles of rotation of ray D for sugar solutions of various degrees of concentration, in 2 decimetre tubes are given, from which, by interpolating for the decimal figures, it appears that to give an angle of rotation of 21*67, a solution must contain 16*302 grammes of sugar in 100 cubic centimetres. This concentra- tion, it will be seen from the table already given, 82, corresponds with a reading of 62*662 divisions on Ventzke's scale. It is evident, therefore, that by dividing the angular values 21*67 and 24*5 by that number we obtain the value of 1 Ventzke. Thus : 1 Ventzke (ray/) = 0-3458 angular degrees (ray D), 1 Ventzke (ray/) = 0'3910 angular degrees (ray /), values which agree almost exactly with those previously obtained. 84. Correction of Errors due to Imperfect Construction. In using a new instrument, it is necessary previously to test the correctness of the scale. When the zero-point of the instrument has been carefully fixed, and brought, by means of the adjust- 170 PRACTICAL APPLICATIONS OF ROTATORY POWER. ment screw, to coincide exactly with, the zero-point of the graduation, the introduction of a 2 decimetre tube filled with a solution of 26*048 grammes of sugar in 100 cubic centimetres, should give a rotation of exactly 100 on the scale. For this experiment it is necessary to use specially prepared pure sugar only. The best refined still contains from O'l to 0'2 per cent, of inorganic matter, and does not record more than 99 '8 to 99 -9. In sugar-candy, the frequent presence of invert- sugar, recognizable by its reduction of Fehling's copper solution, causes it to record a rotation likewise too low. To obtain a pure material, sugar-candy should be repeatedly crystallized from alcohol of about 85 per cent. Or it may be prepared by putting one part sugar-candy in half its weight of water and heating till it dissolves, filtering the hot solution into a porcelain dish, adding two parts absolute alcohol, and stirring frequently till it cools. The sugar crystallizes out as a fine powder, which should then be brought upon a filter and washed, first with, dilute, then with strong alcohol, and dried at a temperature of about 60 Cent. The product thus obtained does not yield more than about 0*005 per cent, of ash, and has no action on Fehling's solution. If now a solution of 26 '048 grammes of sugar so purified does not give a rotation of exactly 100 divisions of the scale, the reading being either too high or too low, it will be necessary, before using the instrument, to determine the particular normal sugar weight belonging to it. Suppose, for instance, that the above solution has given the reading 100*3 on the scale, the sugar-percentage answering to a reading of 100 must be determined from the proportion 100*3 : 26*048 grammes = 100 : x whence x = 25*970 grammes. So that in all applications of the instrument the normal weight must be taken as 25*970 instead of 26*048 grammes, and 1 of the scale must be understood to indicate 0*2597 gramme sugar in 100 cubic centimetres solution. In this way accurate results can be obtained with such an instrument, but it presents the disadvantage that all tables calculated for the number 26*048 are useless, and must be reconstructed. If the 100 point has been found in its proper place, still the scale, which, is supposed to be equally graduated throughout its length, must be tested at a few other points as well. DETERMINATION OF CANE-SUGAR. 171 Proceeding, according to Schmitz's table, given in 82, solutions are prepared containing respectively 19*519, 13*003, and 6*496 grammes of pure sugar, which should give rotations of 75, 50, and 25 respectively. If, however, important discrepancies should occur in the readings, then it becomes necessary to prepare a whole series of solutions of known saccharine strengths, note the degrees of rotation indicated by each, and then draw up a special correction- table for the instrument. This is best done by the graphic method. Errors of this kind appear when the four faces of the two quartz wedges of the compensator have not been ground perfectly true, so that differences in the total thicknesses of the compensators, produced bv the sliding of the wedges, are not perfectly proportional to the differences of reading on the scale. Scheibler l has given a method by which such errors, which are of frequent occurrence, can be eli- minated, at least when we are dealing with rotations exceeding 80. This, the so-called method of double observation, most generally used in the analysis of natural sugars, is as follows : A sample of 26*048 grammes is made into a 100 cubic centimetre solution, or more commonly 13*024 grammes are taken and a 50 cubic centimetre solution prepared, and the rotation observed in a 2 decimetre tube in the ordinary way. If the degrees indicated be, let us say, 94*2 (which should therefore be the sugar-percentage), this result will be correct provided the quartz wedges at the point corresponding to this reading are of the proper thickness. To test this, we must calculate the concentration required to give a rotation of 100 by the proportion 94*2 : 13*024 = 100 : x whence x = 13*82*6. A 50 cubic centimetre solution must then be prepared with 13*826 grammes of the sugar to be analyzed, and the rotation observed in a 2 decimetre tube. If it gives 100 on the scale, the first result, 94*2 per cent., is correct. If, however, the second solution does not give exactly 100, but some less number, as 99'6, in that case the result of the first observa- tion is incorrect. The correct sugar-percentage can, however, be easily ascertained, as it must stand in the proportion 13-826 : 99*6 - 13*024 : x x = 93*8. The true sugar-percentage isaccordingly 93'8, and the number of degrees indicated on the scale in the first experiment (94'2) was 0*4 too high. 1 Scheibler: Zeitsck. des Vereins fur Rubcnzuclcerindmtrie, 1870, 212; 1871, 318. 172 PRACTICAL APPLICATIONS OF ROTATORY POWER. If, again, the second experiment gives, say, 100'2 instead of 100, the proportion will then stand : 13-826 : 100-2 = 13-024 : x, and the correct sugar-percentage will be x 94'4 per cent. In this way errors arising from imperfect construction of the quartz wedges can be eliminated, and as the second observation invariably lies close to the 100 point, the position of which has already been accurately fixed, it is found that the results given by different instru- ments correspond within + O'l per cent., while by the ordinary method the differences between them may be much greater. As to the effect of the imperfect proportion between rotation and concentration upon this method, we have already said ( 82) that when we are dealing with, sugar-percentages recording more than 84, such as we find in crude sugars, it may be neglected. When, however, the solutions indicate deviations ranging from 30 to 76, this is no longer the case, and the method of double observation fails to afford correct results. It will be seen from the foregoing remarks that the quartz-com- pensation principle in polariscope instruments involves considerable difficulties. Errors and corrections, like those just mentioned, do not occur in instruments with rotating Nicols (Wild's and Laurent's); moreover, these give generally more accurate results. 1 For the method of verifying the length of solution-tubes see 66. For the influence of glass end-plates see 64. 85. Influence of Temperature on Determinations loy the Sac- charimeter. The normal temperature at which the determination of the 100 point is made being 17'5 Cent. (63'5 F.), the experiments will ordinarily be made at some other temperature ; for the experi- mental tubes not being usually provided with water-jackets, but exposed to the air, are subject to any variations in the temperature of the apartment. It is true, indeed, as Tuchschmid's 2 researches have shown, that the specific rotatory power of sugar is not in itself affected by heat, but the directly observed deviation is influenced thereby. Thus, when the temperature rises, the length of the tube, 1 Schmidt and Haensch, opticians, Berlin, have lately brought out a half-shade in- strument, with quartz- wedge compensators and Ventzke's scale. This instrument admits of much more accurate adjustment than the usual bi-quartz colour instrument. The variations do not exceed O'l division and they can be used by colour-blind persons. 3 Tuchschmid : Journ. fiir prakt. C/wm., New Ser. 2, 235. DETERMINATION OF CANE-SUGAR. 173 on the one hand, is increased, while, on the other, the density of the contained solution is reduced "by its increase of volume. The former tends to increase the deviation, but this tendency is overpowered by the larger decrease due to the latter. Mategczek, 1 taking as his basis the dilatation-coefficient of glass, 66, along with Gerlach's 2 re- searches on the density of saccharine solutions at different tempera- tures, has calculated the variations arising from this source. He gives a table for Ventzke's scale, of which the following is an abridgment : Grammes of Saccharimeter degrees Sugar in 100 cub. cent, of Temperature. recorded by a Solution normal at 17"5 Solution, corresponding to 1 degree on Cent. the Scale. 10 100-17 0-26004 11 100-14 0-26010 12 100-12 0-26016 13 100-10 0-26022 14 100-08 0-26028 15 100-05 0-26034 16 100-03 0-26039 17 100-01 0-26045 17-5 100-00 0-26048 18 99-99 0-26051 19 99-96 0-26057 20 99-94 0-26064 21 99-91 0-26071 22 99-88 0-26078 . 23 99-85 0-26086 24 99-83 0-26093 25 99-80 0-26100 26 99-77 0-26108 27 99-74 0-26116 2S 99-71 0-26124 29 99-68 0-26132 30 99-65 0-26139 1 IMategczck : Zcitsch. dcs Vercins fiir Rubenzncleerindustric, 1875, 877. 2 Gerlach: Idem., 1862. 283. 174 PRACTICAL APPLICATIONS OF ROTATORY POWER. Hence, for example, if a thermometer plunged in the contents of the tube, after the rotation has been observed, indicates, say 20, then, in calculating the sugar-percentage, the constant 0'26064 must be used instead of '26048. (b.) The Soleil-Duboscq Saccharimeter. 86. The original Soleil instrument, as used in France, and manufactured at the optical instrument works of J. Duboscq, Paris, agrees essentially in principle with that just described, except as regards the scale. This is so devised that the deviation produced by introducing a plate of dextro-rotatory quartz 1 millimetre thick is taken as a fixed point, and the space between this and the zero-point is divided into 100 equal parts. Now, according to Clerget, 1 the same amount of deviation is produced by a 2 decimetre column of a sugar solution containing 16'471 grammes in 100 cubic centimetres. This concentration was subsequently corrected by Duboscq 3 to 16'350 grammes, and the scales for this instrument are now so constructed that the 100 point is recorded by a solution containing 16*350 grammes of pure dry sugar-candy in 100 cubic centimetres. Con- sequently each degree of the scale represents 0'1635 gramme in 100 cubic centimetres. In construction, the French-made instruments differ from the German (Ventzke-Scheibler) in having both quartz wedges movable. Besides this, the regulator for producing the transition-tint is placed in the eye-piece of the instrument, with its Nicol immediately behind the eye-glass of the telescope, and capable of partial rotation by means of a rim projecting through the telescope tube. In using this form of instrument, 16'35 grammes of the sub- stance to be examined are weighed, made into a 100 cubic centi- metre solution, and the solution examined in a 2 decimetre tube. The degrees of rotation on the scale indicate directly the number of grammes of sugar in 100 cubic centimetres. In other respects, the method of observation is precisely the same as in using the Soleil- Yentzke-Scheibler saccharimeter. To avoid errors from imperfect 1 Clerget : Ann. Chim. Phys., [3] 26, 175. 2 According to the still later researches of Schmitz and Tollens, a still more correct value for this constant is 16*302 grammes. (From the equation for c, given on p. 180). DETERMINATION OF CANE-SUGAR. 175 quartz-wedges, Scheibler's method of double observation for the 100 point may likewise be adopted. In using Soleil's saccharimeter for the approximate determination of the specific rotation of other substances, the deviation of which has to be reckoned in angular measure, one has simply to bear in mind that, according to 18, a quartz plate 1 millimetre thick rotates ray D through an angle of 2r67,^and mean yellow light (ray /) through 24-5, or, 1 Soleil (ray j) = 0*2167 angular degrees (ray -Z)), 1 Soleil (ray,/) = 0'245 angular degrees (ray/). 87. Correction for -imperfect proportionality between deviation and concentration will also require to be made in using the Soleil- Duboscq. The amount of correction necessary is given for every 10 in the table annexed: Degrees on Scale. Corrected Reading. Difference. Grammes of Sugar in 100 cubic centi- metres Solution. Uncorrected. Corrected, j Difference. 100 100-00 o-oo 16-350 16-350 o-ooo 90 89-98 0-02 14-715 14-712 0-003 80 79-97 0-C3 13-080 13-075 0-005 70 69-96 004 11-445 11-438 0-007 60 59-95 0-05 9-810 9802 0-008 50 49-95 0-05 8-175 8-167 0-008 40 39-95 0-05 6-540 6-532 0-008 30 29-96 0.04 4-905 4'898 0-007 20 19-97 0-03 3-270 3-265 0-005 10 9-98 0-02 1-635 1-632 0-003 As to the influence of temperature upon determinations by this instrument, Mategczek l gives a table from which the follow- ing is an extract : Mategczek: Zeitsch. des Vcreinsfur Riibcnzuckcr Industrie, 1875, 891. 176 PRACTICAL APPLICATIONS OF ROTATORY POWER. Grammes of Sugar Tempera- Degrees in 100 cub. cent. ture. observed. corresponding to 1 degree. 15 100-05 0-16341 16 100-03 0-16344 17 100-01 0-16348 17-5 100-00 0-16350 18 99-99 0-16352 19 99-96 0-16356 20 99-94 0-16360 21 99-92 0-16363 22 99-89 0-16367 23 99-87 0-16371 24 99-85 0-16375 25 99-82 0-16378 (c.) Wild's Polariscopc, with Sazcharimctric Scale. 88. Wild's polariscope, already described ( 49), can be fitted with a scale for use as a saccharimeter. As supplied from the works of Hermann and Pfister, of Berne, these instruments have a scale divided into 400 equal parts, and their construction is based upon the specific rotation of cane-sugar, [a] D = 66 '417, as determined by Wild 1 in a solution containing 30*276 grammes of cane-sugar per 100 cubic centimetres. Then assuming the amounts of concentra- tion and of rotation to be strictly proportional, he calculates the value of the angle of rotation a, which a solution containing 40 grammes of sugar in 100 cubic centimetres should give in a 2 deci- metre tube. The equation ^ x 4Q = 66417, gives a = 53134. Accordingly, an angle of this amount, measured from one of the zero- points of the instrument, is divided into 400 equal parts, so that, tak- 1 "Wild: Weber ein neues Polaristrobometer u. eine neue Bestimmung der Drehnngs- contante des Zuckers. Berne : 1865. Also, Melanges Phys. et Chim. Bull, de V Acad. de tit. Petcrsbourg, 8, 33. DETERMINATION OF CANE-SUGAR. V /\ ifr** S , ^^T/r ^ ing observations with a 2 decimetre tube, each division of the scale * : will represent 1 gramme of sugar in 1 litre of solution. The useoF""" a sodium flame is here presupposed. According to this mode of graduating the scale, a solution containing 10 grammes of pure sugar in 100 cubic centimetres, observed in a 2 decimetre tube, should record 100 degrees, each divison of the scale indicating 1 per cent, of sugar. If a solution of 20 grammes of sugar in 100 cubic centi- metres be used, the amount recorded should be 200 degrees, each division of the scale corresponding to one half per cent, of sugar, and so on for solutions containing up to 40 grammes of sugar. Thus any weight of sugar may be chosen as normal weight, but a solution of 20 grammes in 100 cubic centimetres, or 10 grammes in 50 cubic centimetres, will be found most convenient. The observed rotation must then be divided by 2, and as with a little practice the scale can be read to one-fifth of a division, we can bring out values to O'l per cent. For example, if a solution of 20 grammes of a crude sugar in a 2 decimetre tube recorded 184'6 degrees, the percentage weight of sugar would be 92*3. In dealing with substances of low sugar-percentage, such as beet-root juice, it is more convenient to weigh out as much as 60 or 80 grammes, and dilute to 100 cubic centimetres. The degrees recorded must then, of course, be divided by 6 or 8 to get the correct sugar-percentage. The greater the weight of substance taken for solution, the greater will be the accuracy of the deter- mination. In other respects, the mode of observation is similar to that described in 51. The lamp, figured in 46, with a bead of salt or soda, can be employed as the source of light. To convert the readings on the saccharimetric scale into angular measure, we have only to remember that as an angle of 53'134 was divided into 400 equal parts, 1 of the scale = 0*1328 angular degrees. 89. The effect of inconstancy of specific rotation on the saccha- rimetric scale is shown in the annexed table of corrections, calculated by Schmitz, 1 and based on the assumption that a solution containing 20 grammes of pure sugar records exactly 200 degrees. 1 Schmitz: Ztifsch. des Vcreins fur RubenzucJcerindustrie, 1878, 48. 178 PRACTICAL APPLICATIONS OF ROTATORY POWER. Divisions of Scale. Grammes of Sugar in 100 cub. cents, of Solution (Calculated). 200 20 190 19 180 18 170 17 160 16 150 15 140 14 130 13 120 12 110 11 100 10 90 9 80 8 70 7 60 6 50 5 40 4 30 3 20 2 10 1 Grammes of Percentage of Sugar by weighing Sugar in 100 out 20 grammes of Substance. cub. cents, of Solution (Corrected). Uncorrected. Corrected. 20-000 100 100 18-997 95 94-99 17-995 90 89-98 16-993 85 84-97 15-992 80 79-96 14-990 75 74-95 13-989 70 69-95 12-988 65 64-94 11-988 60 59-94 10-987 55 54-94 9-987 50 49-94 8-987 45 44-94 7-988 40 39-94 6-988 35 34-94 5-989 30 29-95 4-991 25 24-95 3-992 20 19-96 2-993 15 14-97 1-995 10 9-98 0-998 5 4-99 It will be seen from the two last columns that no correction is needed for percentages under 20 or over 80, the error in such cases not affecting the results to the amount of a tenth per cent. For per- centages between 25 and 75, the indications directly observed are from 0-05 to 0*06 too high. (d.) Saccharimeter with Angular Graduation on Mitschcrlicli'x, Wild 's or Laurent's Principle. 90. Any one of the forms of polariscope described in 45, 49 and 57 may be used for determining the concentration c of a given DETERMINATION OF C AXE-SUGAR. 179 sugar-solution by observing the angle of rotation a for a column / deci- metres long, and substituting values in the equation : fOOa Disregarding the variation of specific rotation [a] with the con- centration of the solutions, a mean value may be assigned to it, which will serve for most of the sugar-solutions met with in practice. For example, by adopting, in analyses of natural sugars and their refined products, a normal solution of 15 grammes in 100 cubic centimetres, we shall obtain percentages ranging between 80 and 100, and the mean concentration c = 14 grammes. But according to the observations of Schmitz and Tollens recorded in 91, c = 14 should yield an angle, which by the above equation corresponds to a specific rotation [a] D = 66*50. Introducing this value for [a] in the equa- tion, we get the annexed formula for determining the number of grammes of sugar in 100 cubic centimetres solution : c = 1-504 4-, l in which a is the angle of rotation observed with the sodium light, and / the length of tube employed. With a 2 decimetre tube c = 0752 a. In many cases this maj r be simplified to 0*75, Thus a solution of 15 grammes of pure sugar should give a rotation of 20 exactly. When, therefore, 15 grammes of any saccharine (natural sugar) are made into a 100 cubic centimetre solution, and the angle of rotation observed in a 2 decimetre tube, the sugar percentages may be obtained by simply multiplying by 5. In weighing out any other number of grammes, P 9 of substance the percentage can be calculated from the observed deviation a from the proportion P : 0-752 a = 100 : #. 91. Here, again, in exact determinations the imperfect propor- tionality between the angle of rotation and the concentration must be taken into account. Schmitz has prepared a table based upon the following observations, 1 partly his own and partly those of Tollens, 3 at a temperature of 20 Cent. 3 1 Schmitz : Zeitsch. des Vereins fur Rubenztcckerindustrie, 1878, 53 and 58. 3 Tollens: Ber. der deutsch. chem. Gesettsch. 10, 1403. 3 The angles of rotation were all observed at 20 Cent. ; the concentrations by Schmitz at 20 Cent., those by Tollens at 17'5 Cent. The latter trifling difference does not affect the results. >* 180 PRACTICAL APPLICATIONS OF ROTATORY POWER. Number of Solution. Grammes of Sugar in 100 cub. cents, of Solution. Grammes of Sugar in 100 grammes Solution. Observed angle of Rotation with a 2 -decimetre Tube. Observer. c. P- a. 1 2-014 2-000 2-69 Schmitz 2 4-460 4-384 5-93 Tollens 3 5-096 5-000 6-78 ' Schmitz 4 8-195 7-945 10-92 Tollens 5 10-399 10-004 13-82 Schmitz 6 15-010 14-200 19-94 Tollens 7 18-175 16-999 24-13 Schmitz 8 27-641 25-010 36-67 Schmitz 9 31-151 27-803 41-26 Tollens 10 40-175 34-833 53-29 Tollens 11 47-120 39-988 62-35 Schmitz 12 54-132 44-914 71-65 Tollens Hence the following interpolation- for mulse for determining from the observed angle of rotation a the concentration c and percentage p of solutions have been derived by the method of least squares : c = 075063 a + 0-0000766 a 2 , p = 074730 a - 0-001723 a 2 . From these equations the annexed table has been prepared : l Observed Grammes Difference Observed Grammes Differ- Rotation of Sugar in for 0-1 Rotation of Sugar in ence for with 2 -deci- 100 cub. cents. of with 2-deci- 100 grammes 0-1 of metre Tube. Solution. Rotation metre Tube. Solution. Rota- a. c. a. p. tion. 1 0-751 ) 1 0-745 0-074 2 1-501 2 1-488 0-074 3 2-253 0-075 1 3 2-226 0-073 4 3-004 j 4 2-961 0-073 1 The value p is for solutions of pure sugar. In beet-root solutions where other substances are present, the sugar-percentages must be determined from the values for c, and the observed specific gravity of the solutions. DETERMINATION OF CANE-SUGAR. 181 Observed Rotation with 2 -deci- metre Tube, a. Grammes of Sugar in 100 cub. cents. Solution. c. Difference for 0-1 of Rotation. Observed Rotation with 2 -deci- metre Tube, a. Grammes of Sugar in 100 grammes Solution. P- Differ- ence for 0-1 of Rota- tion. 5 6 3-755 4-507 | 5 6 3-693 4-422 0-073 0-073 7 5-259 7 5-147 0-072 8 6-010 8 5-868 0-072 9 6-762 9 6-586 0-072 10 7-514 10 7-301 0-071 11 8-266 11 8-011 0-071 12 9-019 12 ' 8-719 0-071 13 9-771 13 9-424 0-070 14 15 10-524 11-277 \ 0-075 14 15 10-124 10-821 0-070 0-070 16 12-030 16 11-516 0-069 17 12-783 17 12-206 0-069 18 13-536 18 12-893 0-068 19 14-290 19 13-576 0-068 20 15-044 20 14-257 0-068 21 15-797 21 14-933 0-067 22 16-551 22 15-606 0-067 23 17-306 23 16-277 0-067 24 18-059 , 24 16-943 0-066 25 18-814 25 17-605 0-066 26 19-568 26 18-265 0-066 27 20-323 27 18-921 0-065 28 21-078 28 19-573 0-065 29 21-833 29 20-223 0-065 30 22-588 30 20-868 0-064 31 32 23-343 24-098 > 0-076 31 32 21-510 22-149 0-064 0-064 33 24-853 33 22-784 0-063 34 25-611 34' 23-416 0-063 35 26-366 35 24-044 0-068 36 27-122 36 24-670 0-068 37 27-878 37 25-291 0-062 38 28-635 38 25-909 0-062 39 29-392 39 26-523 0-061 182 PRACTICAL APPLICATIONS OF ROTATORY TOWER. Observed Grammes Difference Observed Rotation of Sugar in for 0-1 Rotation with 2 -deci- 100 cub. cents. of with 2 -deci- metre Tube. Solution. Rotation. metre Tube. a. c. a. 40 30-148 \ 40 41 30-905 41 42 31-662 42 43 32-420 43 44 33-176 44 45' J 33-933 45 / 0-076 46 . 34-601 46 47 35'449 47 48 36-207 48 49 36-96G 49 50 37-724 50 Grammes Differ- of Sugar in ence for 100 grammes 0-1 of Solution. Rota- ? tion. 27-134 0-061 27-743 0-061 28-347 0-060 28-948 0-060 29-545 0-060 30-139 0-0-39 30-729 0-059 31-317 0-059 31-900 0-058 32-481 0-058 33-057 0-058 For example, suppose an angle of 16'4 has been observed, we see that 16 = 12'030 and 0*4 = 4 x 0*075, hence the solution con- tains in 100 cubic centimetres 12'330 grammes of sugar. (The constant 0752 given in 90 would show a concentration of 12'333, and its approximate value 0'75, a concentration of 12"300.) Again, 100 parts by weight of the same solution, since 16 1T516 and 0'4 = 4 x 0'069, contain 11*792 parts by weight of sugar. As regards the influence of temperature, the researches of Tuchschmid and the calculations of Mategczek ( 85) show that when the concentra- tion amounts to about 25 grammes of sugar in 100 cubic centimetres, and observations are taken between 15 and 25 Cent, in glass tubes 2 decimetres long, a rise of 1 Cent, causes a decrease of O'Oll angular measure. Thus, when the temperature of observation differs from 20 Cent., the foregoing value may be used to correct the angle of rotation observed. For example, suppose the temperature of the solution were 17 Cent., the amount 3 x O'Oll must be subtracted, or if the tempera- ture were 23 Cent., the same amount must be added to the angle observed. For sugar-solutions of less concentration, the amount of this correction is less, and when the temperature is not far removed from 20 Cent, it may be neglected altogether. DETERMINATION OF CANE-SUGAR. 183 (e.) Preparation of Solutions for the Saccharimeter. 92. In saccharimetry, measuring flasks of 50 and 100 cubic centimetres are employed which are usually provided with an addi- tional mark, indicating capacities of 55 and 110 cubic centimetres respectively. These marks are fixed by weighing into the flasks water at some determinate mean temperature, usually 17J Cent. (63 J Fahr., 14 Reaum.). As will be seen from the table given in 73, page 146, the following weights of water must be introduced in order to fix the levels of the several marks : For the 50 cubic centimetre mark, 49-938 grammes. 55 54-932 100 99-875 110 109-863 The correction for weight in vacuo is here disregarded. 1 The solutions necessary for the different forms of saccharimeter, taking observations in each case with 200 millimetre tubes, are as given below : 50 cubic centimetres will generally be found sufficient. Saccharimeter. Weight of Substance required for Prepara- tion of : 100 cubic centimetre Solution. 50 cubic centimetre Solution. Solcil-Ventzke-Scheibler . . . i. L '.. t> 26*048 grammes 16-35 20 15 13 '024 grammes 8-175 10 7-5 Wild, with Saccharhnetric scale .,-.;,, Mitscherlich, Wild, and Laurent, with an ocular raduation . For weighing the samples, Scheibler 3 recommends basins with a lip made of German silver, a material not readily wetted by aqueous liquids. 1 Reduced to vacuo, the weights required, according to 69, are for the 50 cubic centimetre mark, 49-888 grammes, and for the 100 cubic centimetre mark, 99'775 grammes of water at a temperature of 17^ Cent. ' z Scheibler: Zeitsch. des Vereins fur Riibcnzucker Industrie, 1870,614. 184 PRACTICAL APPLICATIONS OF ROTATORY POWER. The weighed substance should be dissolved directly in the basin, the contents poured into the flask, and the basin itself then carefully washed with a stream of water into the flask, care being taken that the latter does not get more than three-quarters filled. 93. Decoloration of Solutions. If the solution so prepared, as is usually the case with natural sugars, beet-juice, and the like, is more or less coloured and turbid, the addition of some clarifying substance becomes necessary. The substance most commonly employed for the purpose is basic acetate of lead, in quantities of one or more cubic centimetres, according to the impurity of the sugar and the concentration of the solution. This usually throws down a heavy precipitate, by which various non-saccharine substances t as malic acid, aspartic acid, etc., are removed as lead salts, carrying down with them the particles which produce the turbidity. If the precipi- tate formed is small, it is convenient to add besides a few drops of solution of alum, so as to produce a precipitate of sulphate of lead. Too great excess of the basic acetate must be avoided, otherwise the filtered liquid will, in contact with the air, again become cloudy by the formation of carbonate of lead. This turbidity may, however, be dispelled by the addition of a drop of acetic acid. The basic acetate of lead is prepared by putting a finely powdered mixture of 3 parts ordinary acetate of lead and 1 part litharge along with 10 parts water in a closed flask, and allowing the mixture to remain until, aided by frequent shaking, only a small white residue remains undissolved. The filtered liquid should then have a specific gravity of from 1'23 to T24. Aluminium hydrate, as recommended by Scheibler, 1 can also be employed as a decolorant. This can be prepared by precipitating a solution of sulphate of aluminium or of alum by means of ammonia, and washing the precipitate by decantation until the wash- water no longer gives a blue colour to red litmus paper. The voluminous pulpy mass so obtained is to be preserved in a closed flask, from which, by means of a pipette with wide stem, quantities may be removed as required. For the clarification of 13'024 grammes of a sugar dissolved in a 50 cubic centimetre flask, from 3 to 5 cubic centimetres are generally required. The alumina is especially adapted for the removal of tur- bidity ; but less so for the removal of colouring matters ; and thcre- 1 Scheibler: Zeilsch. den Vereinsfiir Riilenziicker Industrie, 1870, 223. DETERMINATION OF CANE-SUGAR. 185 fore we may add besides, if necessary, some basic acetate of lead and a little alum-solution. After introducing the clarifier, the contents of the flask are made to mix by a gentle motion, and then left undisturbed for five to ten minutes. The surface of the liquid is then brought to the mark by adding water from the wash-bottle. If foam forms on the surface of the solution and prevents the exact adjustment of the level, it can be removed by touching it with a drop of ether or by merely pouring upon it a small quantity of ether- vapour from the bottle (Scheibler). The flask is then closed with the thumb and shaken vigorously for some time, after which the mixture is to be filtered. For this purpose round filters 13 to 14 centimetres (about 5J inches) diameter, which will easily take 50 cubic centimetres, should be used. Of course, they must not be yvetted before use, and the funnel and receiver below must be perfectly dry. Evaporation must be prevented during filtration by covering the funnel and receiver with glass plates. Very often the first few drops of the filtrate are turbid, and should be received in another vessel. The clear solution should at once be put into the polariscope- tube. The mode of using flasks with double marks (as 50 and 55 cubic centimetres) is as follows : The sugar-solution is made up to the 50 cubic centimetre mark, the acetate of lead, etc., added to the upper mark and the flask then shaken, etc., as before. The solution is then too dilute by one-tenth of its volume, and the angle of rotation observed in a 200 millimetre tube must be increased by one-tenth to get the correct value; or the rotation may be directly observed in a tube 220 millimetres long a tube of this size being sometimes supplied with the instru- ment. On the other hand, in using flasks with single marks only, an error occurs whenever the addition of basic acetate of lead produces a precipitate, from the diminution thereby caused in the volume of liquid contained by the flask, when the mixture stands at the 50 cubic centi- metre or 100 cubic centimetre mark. The liquid will then be too concentrated, and its rotatory power too high. The error from this source will obviously vary in magnitude, with the amount of precipitate furnished by different saccharine products. Scheibler 1 examined by a variety of methods the volume of the precipitate obtained in the deco- loration of 100 cubic centimetres of beet-root liquors with 10 cubic centi- metres of basic acetate of lead. His experiments showed a mean value 1 Scheibler: Zeitsch. des Vereins fur Rtibcnzucker Industrie, 1875, 1054. 186 PRACTICAL APPLICATIONS OF ROTATORY POWER. of 1'3 cubic centimetres. Hence sugar-percentages, estimated from the observed rotation, appear 0*15 per cent, too high. According toNebel and Sostmann, 1 the error in beet-juices averages 0'17 ; in diffusion- juices 0'27 per cent. Pellet 3 obtained the following error- values : For beet-juices 0'15 to 0'2 per cent. ; cane-sugar juices O'l per cent. ; thick syrups, 0*25 per cent. ; sugars from the second and third crops, - 25 per cent.; molasses, 0*63 per cent. Accordingly, the results obtained by direct observation must be reduced by the above amounts to get the true sugar-percentages. 94. Sometimes, indeed, as in the case of molasses and dark- coloured bye-products, the colour is so intense that even the basic acetate of lead fails to sufficiently decolorize the solution. In such cases an attempt should be made to observe the rotation by employ- ing a 100 millimetre tube, or by diluting the solution to double its original volume, the observed rotation being, of course, doubled. Where this is found impracticable the solutions should be cleared with animal charcoal after preliminary treatment with acetate of lead. For this purpose, 30 to 40 cubic centimetres of the filtrate are placed in a flask, with 3 to 6 grammes of powdered and strongly dried bone-charcoal, and either shaken vigorously for some time or allowed to stand for twelve to twenty-four hours. In most cases, we shall then obtain, after filtration, a perfectly clear liquid. The charcoal has, however, the disadvantage of abstracting not only colouring matter, but some sugar as well, so that the rotation results will be considerably too small. It will be necessary, there- fore, in order to apply the proper correction, to make a preliminary determination of the absorptive power of the particular charcoal used, by a few experiments with sugar-solutions of known strength. Thus, Scheibler 3 found that, with 50 cubic centimetre solutions, con- taining 13*024 grammes of various natural sugars, cleared with basic acetate, after standing over 5*5 grammes of desiccated bone-charcoal for from twelve to twenty-four hours, the observed rotation gave sugar- percentages averaging 0'4 to 0'5 too low. He also showed that the amount of sugar absorbed is proportional to the quantity of charcoal used. 1 Nebel and Sostmann : Zcitsch. des Vereinsfur Rubenzmker Industrie, 1876, 724. 2 Pellet: Idem., 1S7G, 730. 3 Scheibler: Idem., 1870, 218. DETERMINATION OF CANE-SUGAR. 187 (f.) Determination of Cane-Sugar in the Presence of other Active Substances. 95. Another source of inaccuracy met with in the sacchari- metric analyses of beet-liquors, inferior natural sugars, and molasses, is the occurrence along with cane-sugar of a whole series of other substances, capable of affecting in different ways the plane of polariza- tion of light. Of such substances the following have been found, viz. : Malic acid ( ), asparagin and aspartic acid (both + in acid solutions and in alkaline), glutamic acid (. + ), invert-sugar ( ), beet-gum ( ), dextran ( + ), the two last-named possessing very high rotatory powers. In molasses these substances may be present in such quantity as to render the determination of the sugar in the highest degree inaccurate, and even with beet-liquors some uncer- tainty is thereby involved in the results. It is true that by clearing with basic acetate of lead such substances are precipitated in part ; but a method of certainly removing them entirely or of optically neu- tralizing them is stil] a desideratum. Eisfeldt and Follenius 1 attempt this, by heating with a solution of copper sulphate and caustic soda, so as partly to precipitate and partly decompose them by oxidation. Sickel 2 has proposed a method, which consists in adding to 13*024 grammes of beet-juice 1 cubic centimetre of basic acetate of lead, and diluting to 50 cubic centimetres with absolute alcohol. In this way the asparagin, aspartic acid, malic acid, gum, and dextran are precipi- tated, and the rotatory power of the invert-sugar almost completely annulled by the presence of the alcohol. This method appears to be serviceable, but requires further confirmation. 96. When invert-sugar alone accompanies the cane-sugar, the effect of which is to reduce the rotation, the correct percentage of the cane-sugar present can be determined by employing the so-called inversion method of Clerget. 3 When a saccharimeter with Soleil scale is used, the method is as follows : The usual normal solution, containing 16'35 grammes of the sugar is prepared in the ordinary way, cleared, if necessary, with basic acetate of lead, and the rotation determined. Then 50 cubic centimetres of the solution 1 Eisfeldt arid Follenius : Zeltsch. des Vereins fur RubenzucJcerindustrw, 1877, 728 and 794. 3 Sickel: Idem., 1877, 779 and 800. 3 Clerget: Ann. Chim. Phy*. [3], 26, 175. 188 PRACTICAL APPLICATIONS OF ROTATORY POWER. are heated with 5 cubic centimetres of concentrated hydrochloric acid for ten minutes, on a water-bath at a temperature of about 68 Cent. (154 Fahr.), whereby the whole of the cane-sugar is trans- formed into invert-sugar. After cooling, the rotation (in this case left-handed) is observed in a 220 millimetre tube, the temperature . of the solution being also noted by introducing a thermometer. The calculation of the percentage of cane-sugar from the above two observations is performed in the following manner : According to Clerget's experiments, a solution containing 16*35 grammes of pure sugar in 100 cubic centimetres which indicates a rotation of + 100 with a Soleil saccharimeter will, after inversion, and observed at a temperature of Cent., indicate a rotation of 44 on the scale, the total change of rotation indicated being 144. Moreover, it is found that the amount of Isevo-rotation of a solution of invert-sugar varies very markedly with the temperature of obser- vation. The above solution, for instance, would undergo, for every rise of 1 Cent., a reduction of 0'5 division on the Soleil scale, so that at a temperature t, its amount would be 144 \ t. Putting S for the sum of the opposite sacchari metric readings (the readings before and after inversion), that is, for the total decrease of rotation, and t for the temperature at which the inverted solution is observed, the required percentage of cane-sugar R may be found from the proportion (144 - i /) : 100 = S : R, whence : 7? " 144- J* If, for example, the amounts of rotation were : By direct observation ....... 94-1 right After inversion at temperature 20 Cent. 37 -2 left then S - 131-3 which gives 100 x 131-3 R = - AA __ -j Q = 98'0 per cent, cane-sugar, instead of the incorrect value, 94*1 per cent., directly obtained from the original solution. Tuchschmid 1 has studied minutely the change of rotation pro- duced by the inversion of sugar-solutions, as well as the influence of 1 Tuclischmid : Jo urn. fur prakt. Chem. [2], 2, 235. DETERMINATION OF CANE-SUGAR. 189 temperature, and gives the subjoined formula for the calculation of cane-sugar percentages : ~ 144-16-0-506 t If, instead of SoleiPs sacchariineter, one with angular graduation be employed, Tuchschmid's formula becomes 21-719 S R ~- 31-31-0-11 t' To determine at the same time the percentage of invert-sugar originally present in the substance, the following method can be adopted: As we have already said, a solution of 16 '35 grammes of cane-sugar in 100 cubic centimetres gives, by inversion, a liquid, which at a given temperature, tf, rotates towards the left through (44 \ t) divisions of the scale. Now, since 171 parts of cane-sugar, when treated with acid, yield 180 parts invert-sugar, the above rotation corresponds to a percentage of 17*21 grammes invert-sugar in 100 cubic centimetres. Putting A for the result of direct observation, R for the sugar-percentage found after inversion, and J for the propor- tion of invert-sugar to be determined, we have the proportion 44 - J t : 17-21 = R-A:J, whence, 17-21 (R - A) 44- Taking, as in the former example, A = 94-1, R = 98'0, and assuming the rotation to have been observed, both before and after inversion, at 20 Cent., we get the result : T 17-21 (98-0 94-1) n /= -_^-__ 1 _ ,2-0 per cent. Employing the more exact constants determined by Tuchschmid, we have : 1. For Soleil's saccharimeter : 17-21 (R - A) = 44-16 - 0-506 1. ' 2. For saccharimeters with angular graduation : 17-21 (jB - A) 9-59 - 0-11 t This method will, of course, cease to furnish correct results when other optically-active substances are present in addition to invert- !'') I'HACIKM, AI'IMjr AHO.Y- W* A* this | f.hod i - no| of utility. ITfTfribflffff, the ifiw-i to pfOMM i* convenient for uh' 1 /ar i* or in not contaminated with o It will I"' i. (.own to \><- free of MUCH HubfctanCC* whui 111'; amount > J elation bf-.fVj/-f: an/i the prcHoncc of irnpuritie*. H/ li^ /U< / ' in thi* way dot^ctf :/I tl.f- pretence of dextrin iu natural tugurM, AH the direction of th(j rotatory powor in unaffected when that huh- ' .I.-., th IHJVO- rotation indicated by )u ,lu- 1/1 /I, therefore, aliio the calculated percentage of aaccharoae, wa r = 5J'0 may be taken a* oon*tant. Tutting thin value in tin <<| nation |a| = -7--, we get the subjoined formula for determining the concentration ft, from the angle of rotation a, observed with a tube / decimetre* in length: c = 1*8808 y We are Hupponing here that the angle of rotation i* taken with a MitHchorlicb, Wild, or Laurent polamcopo, and with aodium flame. The temperature of thoholujion rnunt not differ much from 20 Cent. Then, if a 2 decimetre tube be enn c= 0'04:H a. Hence, 1 rotation repro*ontH 0-!) I ; I / ...mrno of ariliydrou* grapc- Nugar in 100 cubic centirnetn-- -t ."lnl.ion. Thii cori*tini u ill : ZeUwh. dc !' / > >' ' i r< dor MM/I, fi/iem. UeMlMi. IM7, i DETERMINATION OF GLUCOSE. 191 for all degrees of rotation up to 15, which is sufficient for most purposes. 98. With higher amounts of concentration (c greater than 14), the specific rotation of glucose undergoes a rather appreciable increase, as will be seen from the table given in 38. In consequence of this variation, it was necessary to construct interpolation-formula) for calculating the degrees of concentration corresponding to various angles of rotation. For this purpose the following observations of Tollens have been taken as a basis : Grammes of Glucose Grammes of Glucose Observed Angle of No. of in 100 cub. cents. in 100 grammes Rotation, o, Solution. Solution. Solution. for I = 2 deci- = c = P metres. 1 9-634 9-292 10-20 2 20-039 18-621 21-38 3 35-898 31-614 38-46 These figures yield the formulae 1 c = 0-94727 a - 0-0004233 a 2 p = 0-94096 a - 0-0031989 a 3 . By means of these, the table given on page 192 has been pre- pared, showing the number of grammes of anhydrous glucose in (1) 100 grammes, and (2) 100 cubic centimetres, of solution, indicated by various angles of rotation observed for ray D, and in a tube 2 deci- metres long. For angles under 10, the constants given in 97 have been employed. 1 The extent to which these formulae agree with other observations made by Tollens, may bo gathered from the annexed table : c c P P a Calculated. Employed. Calculated. Employed. 8-43 7 -96 grm. 7*91 grm. 7'71 grm. 7'68 grm. 11-09 10-45 10-46 ,, 10-04 10-06 ,, 11-72 11-04 11-08 10-59 ,, 10-63 ,, 14-47 13-62 13-60 ,, 12-95 12-95 ,, 192 PRACTICAL APPLICATIONS OF ROTATORY POWEK. Angle of Rota- tion for a Column 2 deci- metres long and Ray D. Grammes of Anhydrous Glucose in 100 grammes Solution. Amount for 0-1 Rotation. Grammes of Anhydrous Glucose in 100 cub. cents. Solution. Amount for 0-1 of Rotation. 1 0-93 0-94 1 2 1-86 0-093 1-89 3 2-79 0-093 2-83 / 0-095 4 3-71 0-092 3-77 5 4-62 0-091 4-72 J 6 5-52 0-090 5-66 7 6-42 0-090 6-60 8 7-32 0-090 7-55 9 8-21 0-089 8-49 10 9-09 0-088 9-43 ) 0-OC4 11 9-96 0-087 10-37 12 10-83 0-087 11-31 13 11-69 0-086 12-24 14 12-55 0-086 13-18 > 15 13-40 0-085 14-11 N 16 14-24 0-084 15-05 17 15-07 0-083 15-98 18 15-90 0-083 16-91 19 16-72 0-082 17-85 20 17-54 0-082 18-78 21 18-35 0-081 19-71 ^ 0-093 22 19-15 0-080 20-64 23 19-95 0-080 21-56 24 20-74 0-079 22-49 25 21-53 0-079 23-42 26 22-30 0-077 24-34 27 23-07 0-077 25-27 23 23-84 0-077 26-19 \ 29 24-60 0-076 27-12 30 25-35 0-075 28-04 31 26-10 0-075 28-96 32 26-84 0-074 29-88 j 0-092 33 27-57 0-073 30-80 34 28-30 0-073 31-72 35 29-02 0-072 32-64 > DETERMINATION OF GLUCOSE. 193 To express the result in terms of glucose-hydrate, C 6 H 12 6 + H 2 O, since the molecular weights, C 6 H 12 6 and C 6 H 12 6 -f H~2 0, are as 180 : 198 or 1 : 1*1, the values found for the anhydride must be increased by one-tenth. 99. Determinations of glucose may also be made with a saccharimeter of quartz- wedge compensation form, as its dispersive power, according to Hoppe-Seyler's l measurements, agrees approxi- mately with that of quartz. In dealing with dilute solutions not containing more than about 10 grammes in 100 cubic centimetres, the specific rotations of cane- and grape-sugars may be assumed to stand in the constant proportion of 66*5 : 53*0. Hence, (1) with Ventzke's scale, in which the 100 point indicates 26'048 grammes of cane-sugar in 100 cubic centimetres, the same amount of rotation 66-5 will, in a solution of grape-sugar, indicate a concentration ^-r . 26'048 = 32*683. This gives 0*3268 gramme of anhydrous glucose for each division of the scale when the rotation is observed in a 2 deci- metre tube. Or, (2) with a Soleil-Duboscq scale, 1 division of the no. K scale will correspond with ^777: . 0*1635 = 0*2051 gramme of anhy- Oo'U drous glucose in 100 cubic centimetres. Thus in the examination of grape-sugars a 100 cubic centimetre solution should be prepared, containing for Ventzke's saccharimeter, 32*68 grammes, forSoleil's 20-51 and observed in a 2 decimetre tube. The number of degrees recorded indicate directly the percentage of anhydrous glucose in the weighed samples. Polariscopes are also constructed on Soleil's principle with scales expressly graduated for grape-sugar. 2 In these so-called diabetometers the index reading gives the number of grammes of glucose in 100 cubic centimetres solution, observed in a tube 1 decimetre long. Where a 2 decimetre tube is used the reading must, of course, be 1 Hoppe-Seyler (Fresenius* , Zeitsch.filr analyt. Chem. 1866, 412) found: We [a] D [], [a],- For glucose (O) .... 42-45 53-45 67'9 81-3 Rotation for 1 millimetre quartz (0) is 17-22 21-67 27'46 32-69 Whence ratio -^- is . . . . 2'46 2-47 2-47 2-49 2 May be obtained of Schmidt and Haensch, Berlin. 194 PRACTICAL APPLICATIONS OF ROTATORY POWER. divided by 2. Usually these instruments have the graduation con- tinued on the other side of the zero-point, so that the scale then serves for determinations of albumen as well, which has a Isevo-rotatory power equal in amount to the dextro-rotatory power of glucose. 100. Determination of Grape-sugar in Diabetic Urine. The urine should, if possible, be examined in its natural state, or if the colour interferes it may be diluted to twice its volume, or observations made with a tube of 1 decimetre length. Turbid urine must of course be filtered. If it be too dark in colour we may take 100 cubic centi- metres, add to it 10 cubic centimetres basic acetate of lead, filter, and examine the filtrate, or we may attempt to decolorize it with animal charcoal. In either case, the urine may lose some of its grape- sugar ; this has been proved to occur when the basic acetate of lead 1 is employed, and is probable in the case of charcoal (compare 94). The presence of albumens, exercising their laovo-rotatory power, may interfere by causing the sugar to appejar too low. They must, therefore, be previously removed. For this purpose, 100 cubic centi- metres of the urine are heated to boiling in a basin, and very dilute acetic acid added till the urine exhibits an acid reaction, and the albumen separates as a flocculent precipitate. It is then filtered, the filter washed, and the filtrate again made up to 100 cubic centimetres ; or, having acidified with acetic acid a determinate volume of the urine, it is mixed with an equal volume of a concentrated solution of sodium sulphate. On boiling the mixture, the albumen separates completely, and can be removed by filtering. Bile-acids, which are dextro-rotatory, are never present in such, urine in sufficient quantity to cause error in the above processes. In ordinary urines, and in general when the proportion of grape-sugar in a urine is less than about 0'2 gramme in 100 cubic centimetres, it can no longer be accurately determined by observing the rotation of the urine itself directly. In such cases, we must take from 1 to 2 litres for an analysis. To this we must add, first, some solution of ordinary acetate of lead, and then, after filtering, some basic acetate together with a little ammonia. The second precipitate will contain the whole of the grape-sugar. It must be filtered off, mixed with alcohol, and excess of lead removed by sulphuretted hydro- gen. The solution separated from the lead sulphide by filtration 1 SecBriicke: Sitzuttgber. tier Wiener Akad. 39, 10. DETERMINATION OF GLUCOSE. 195 must be decolorized with, animal charcoal and concentrated by evapo- ration to a small determinate volume, which can then be placed in the polariscope. By this method, any bile-acids present in the urine pass over into the alcoholic solution finally obtained, and exercise their dextro-rotatory action. Their presence may be detected by evaporating a portion of the solution, dissolving the residue in a little water and mixing with some yeast. In two or three days all the sugar present will be decomposed, so that if, after filtration, the liquor still exhibits dextro-rotatory, power this must be attributed to the presence of bile-acids. 101. The polariscope has also been employed by JNeubauer to detect grape-sugar in " chaptalized " wine. The potato-sugars of commerce invariably contain from 16 to 20 per cent, of imperfectly known substances (amylin of Bechamp), characterized by high dextro- rotatory power, and great resistance to fermentation. When the must has been chaptalized, these substances pass over into the wine. Pure natural wines of moderate age do not contain such substances, and, therefore, when submitted to polariscopic examination in tubes 2 or 2 '2 decimetres in length, either exhibit no rotatory power, or at most a rotation to the right through an angle of 0*1 to 0*4 degree. Choice wines from very highly saccharine must, on the other hand, containing laovulose still unfermented, may appear more or less laevo-rotatory. This is the case with wine " chaptalized " with cane-sugar. The following is the mode of examination recommended by Neubauer : Fifty cubic centimetres of the wine (whether red or white) are placed in a flask with 5 cubic centimetres basic acetate of lead ; some animal charcoal which has been purified by extraction with hydrochloric acid added, and the whole shaken up for a few minutes, and then filtered. The colourless solution is then introduced into the polariscope in a 2 or 2 '2 decimetre tube. If it appears dextro-rotatory to the extent of 1 or more, it may safely be concluded that the wine has been chaptalized with potato- sugar. If, however, the result appears doubtful, 100 to 200 cubic centi- metres of the wine may be concentrated by evaporation to 25 (or 50) 1 Neubauef: Freseniw?, Zeitsch. fl'.r analyt. Chem. 1876, 188; 1877, 201; 1878, 321. o 2 196 PRACTICAL APPLICATIONS OF ROTATORY POWER. cubic centimetres, treated with basic acetate of lead and animal charcoal as before, and the rotation again examined. A rotation of from 1 to 4 at the least will now be obtained if the wine has been chaptalized. When 400 to 500 cubic centimetres of such wines are reduced by evaporation to 50 cubic centimetres, amounts of dextro- rotation of from 5 to 8 are not unfrequently obtained. If the result of the first examination shows a dextro-rotation of not more than 0'4 to 0*6, a further investigation may be made by the following method, which is based on the fact that the unfermentable matters accompanying the potato -sugar are, for the most part, soluble in alcohol, arid can be precipitated therefrom by the addition of ether 250 to 350 cubic centimetres of the wine are first concentrated till the salts crystallize out. This liquid is decanted, decolorized with animal charcoal, diluted to 50 cubic centimetres, and finally filtered. Almost all pure natural wines treated in this way will exhibit a feeble dextro-rotatory power, which in tubes of 2 or 2 '2 decimetres may amount to as much as about 2. Wines that have been chaptalized, on the other hand, yield deviations of from 4 to 11. After this preliminary examination the 50 cubic centimetre solu- tion must be reduced on a water-bath to a syrupy consistency, and alco- hol of 90 per cent, added with constant stirring so long as any deposit forms. The mixture is then allowed to stand for several hours, until the liquid is perfect^ clear, when it is poured off from the generally tough gelatinous residue. If, however, the precipitate formed is flocculent it must be filtered. The precipitate A, and the alcoholic solution B, so obtained are then treated separately as follows : The precipitate A is dissolved in cold water, decolorized with animal charcoal, and filtered. The solution must then be diluted to a volume corresponding with the capacity of the polariscope-tube and placed in the polariscope. In all pure wines, the bulk of the dextro- rotatory substances will be found in this solution, which may therefore give an angle *>f rotation of from 0'5 to 1'8. The alcoholic solution B is evaporated on the water-bath, till about one-fourth of the alcohol originally added remains. This is then placed in a small flask, and after cooling is mixed with from four to six times its volume of ether and vigorously shaken. If after standing the ether is found to have separated from the more or less thick watery liquid beneath, it can be removed by decanting, or by the help of a separating funnel. The watery solution is then diluted somewhat with water, warmed to expel any ether still remaining, and decolorized DETERMINATION OF MILK-SUGAR. 197 with charcoal. The filtrate, which now contains the unfermentable substances in the original potato-sugar, is then examined in a 2 or 22 decimetre tube. If the wine has been chaptalized this filtrate will exhibit dextro-rotation to the extent of from 3 to 11 or more. In pure natural wines of average quality, on the contrary, the filtrate will, in most cases, appear inactive, or may rotate at most from 0*2 to 0'5 to the right. For this optical examination of wines any sensitive polariscope, such as Wild's or Laurent's, may be used. Special polariscopes of simple form (called optical wine-testers) are manu- factured for this purpose at the Optical Institute of Dr. Steeg and Reuter, Homburg v. d. Hdhe. These instruments are in construc- tion essentially similar to that described in 43, Fig. 20. C. Determination of Milk-Sugar. 102. Milk-sugar, C 12 H 22 O n + H 2 0, exhibits, in freshly pre- pared cold solutions, the property known as bi-rotatwn (see 27). The following numbers apply to solutions reduced by heating to constant rotation. Hesse 1 examined four aqueous solutions in a Wild's polariscope with a 2 decimetre tube, and found : for c = 2 an = 2- 144 [a] D = + 53'60 ,, c = 3 3-19 53-16 , c = 5 5-29 52-90 c - 12 12-64 C 52-67' Thus the specific rotation decreases with increased concentration ; but for solutions of the above strengths [a] D = 53 may be taken as the mean value. Moreover, since for each decrease of c by 1, a shows a constant increase of 1*05, the concentration of such solutions may be obtained from the subjoined table, in which : a is the angle of rotation observed in a 2 decimetre tube with sodium light, c the corresponding amount in grammes of milk-sugar (C 12 H 22 O n + H 2 0) in 100 cubic centimetres of solution. ct c. a. c. 1 0-92 7 G-63 2 1-87 8 7-58 3 2-82 9 8-54 4 3-77 10 9-40 5 4-73 11 10-44 6 5-68 12 11-39 1 Hesse: Liebig* s Arw . 176, 93. 198 PRACTICAL APPLICATIONS OF ROTATORY POWER. In observations made with a Ventzke's saccharimeter, and taking for the specific rotation of milk-sugar the constant value of 53, whereby it is made to agree with that of anhydrous glucose, the data afforded by 99 show that each division of the scale will represent 0*3268 gramme of milk-sugar in 100 cubic centimetres solution, as- suming the rotation to have been observed in a 2 decimetre tube. With the French scale the corresponding value is 0'205 gramme. To Determine the Mi/k-sugar in Milk. For this purpose the fat and lasvo-rotatory casein must first be removed. Fifty cubic centimetres of milk are placed in a porcelain basin along with 25 cubic centi- metres of a moderately strong solution of ordinary acetate of lead, heated to the point of incipient boiling, and afterwards allowed to become perfectly cold. The mixture, together with the coagulum, is then poured into a 100 cubic centimetre flask, and water added to bring it up to the mark. After shaking and filtering, the rotation is observed in a 2 decimetre tube, and the result so obtained doubled on account of the solution having been diluted to half its original strength. When the milk exhibits a strong acid reaction, it should first be neutralized with a few drops of soda solution. ' As the volume of pre- cipitate is considerable, the result will be somewhat too high (see 93). D. Determination of Cinchona Alkaloids. 103. The specific rotation of the cinchona alkaloids and of their most important salts has been studied in detail by Hesse. 1 The values so determined serve both as a means of testing the purity of other samples, and in determining the composition of mixtures. Oudemans 2 has also made a number of observations on the same subject. The rotation constants which have been determined with the greatest accuracy are those of quinine, cirichonidine, conchinine (quinidine), and cinchonine. In each of these four alkaloids the specific rotation varies considerably with the nature- of the solvent, and decreases, moreover, with increase of concentration. Hesse has investigated the rotation of solutions containing, according to their respective solvent powers, from 1 to 10 grammes of substance in 100 cubic centimetres of solution, and has found that within these limits the variations are represented by the formula [a] = A B c. As sol- vent, alcohol of 97 per cent, by volume was employed for the pure 1 Hesse: Liebig 1 * Ann. 176, 203; 182, 128. 2 Oudemans: Idem., 182, 33. DETERMINATION OF CINCHONA ALKALOIDS. 199 alkaloids, and for their salts either water, dilute hydrochloric or sulphuric acid of known strength, the latter being added in such quantity that the solutions contained for 1 molecule alkaloid not more than 3 molecules H 01 or H 2 S 4 . This was the proportion of acid used also in the solution of the free alkaloids. In calculating the number of cubic centimetres of standard acid to be added to a given weight of alkaloid, Hesse took 31 b for the molecular weight of all four bases, being the mean of 308 (C 20 H 2 . t N 2 4 , cinchonine and cinchonidine), and 324 (C 20 H 24 N 2 2 , quinine and quinidine) . The error arising from the slight difference from the true molecular weight is trifling. As the rotatory power of solutions containing alkaloids decreases more or less with a rise of temperature, the solutions must be kept at a constant temperature. Hesse took 15 Cent, as a standard. The following tabular arrangement shows the constants obtained by Hesse with preparations of the highest possible degree of purit}^ The numbers have reference 1. To compounds of the alkaloids having the chemical formulae respectively assigned to them (water of crystallization included). 2. To the alkaloid contained in these compounds the latter numbers being calculated from the former. 1 (As in previous cases c stands for the number of grammes of active substance in 100 cubic centimetres of solution ; and for subse- quent reference the formulae are numbered.) Quin ine (Icevo-rotatory) . Quinine hydrate, C 20 H 24 N 2 2 + 3H 2 0. Solution in alcohol 97 per cent, by vol. c = 1 to 10. (1) [a] D = -- (145-2 - 0-657 c). Quinine hydrochhride, C 20 H 24 N 2 2 . H 01 + 2 H 2 0. Solution in water, c = 1 to 3. 1 If [a],/ be the specific rotation of a compound and [a] a that of the active group (e.g., alkaloid) contained in it, then putting M and m as the respective molecular weights : M. = M. * The equation which expresses the value of constant for compounds [a], = A + Be must be transformed for active groups into where c' is the amount of essential active substance (alkaloid) in c parts by weight of the compound. (Hesse : Liebig's Ann. 182, 131.) 200 PRACTICAL APPLICATIONS OF ROTATORY POWER. (2) Compound [o] D = - (144-98 - 315 c). (3) Alkaloid [a] D = - (167-41 - 471 c). Solutions in hydrochloric acid : 1 mol. hydrochloride + 2 mols. H 01, or 1 mol. quinine hydrate + 3 mols. H Cl + water to 100 cub. cent. c = 1 to 7. (4) Hydrochloride [o] D = - (229-46 - 2-21 c). (5) Alkaloid [O]D = -- (28078 - 3-31 c). Quinine sulphate (neutral), 2 (C 20 H 24 N 2 2 ) . H 2 S O 4 + 8 H 2 0. (6) Solution in alcohol of 80 per cent, by vol. c = 2. [o] D = - 162-95. (7) Solution in alcohol of 60 per cent, by vol. c = 2. [a] D = - 166-36. Solution in hydrochloric acid : 1 mol. sulphate + 4 mols. H Cl + water. (8) Anhydrous salt, c = 2. [a] D -- 239'2. Quinine sulphate (mono-acid), (C 20 H 24 N 2 2 ) . H 2 S 4 + 7 H 2 0. Solution in water, c = 1 to 6. , (9) Salt [o] D = - (164-85 - 0'31 c). (10) Alkaloid [a] D = -- (278-71 - 0'89 c). Quinine disulphate (di-acid), (C 20 H 24 JST 2 2 ) . 2 H 2 S 4 + 4 H 2 0. Solution in water, c = 2 to 10. (11) Salt [o] D = -- (155-69 - 1-14 c). (12) Alkaloid [a] D = - (284-48 - 379 c). For the rotation of this salt with 7 mols. H 2 0, see Chapter VII. Solutions in sulphuric acid : I. 1 mol. quinine hydrate -f 3 mols. H 2 S 4 -f water to 100 cub. cent. (13) c = 1 to 5. Hydrate [a] D = - 246'63 - 3-08 c). (14) Alkaloid [a] D = -- 28772 - 419 c).' II. 1 mol. sulphate + 2 mols. H 2 S O 4 + water to 100 cub. cent. (15) c = 1 to 10. Sulphate [a] D = - (171-68 - 078 c). (16) Alkaloid [a] D = - (290'36 - 2'23 c). III. 1 mol. disulphate + 1 mol. H 2 S 4 + water to 100 cub. cent. (17) c = 2 to 6. Disulphate [a] D = -- (] 53-87 - 0'92 c), (18) Alkaloid [a] D = - (281-15 - 311 c). DETERMINATION OF CINCHONA ALKALOIDS. 201 Cinchonidine (Icevo-rotatory) . Cinchonidine, C 20 H 24 N 2 0. Solution in alcohol of 97 per cent, by vol. c = 1 to 5. (19) [a] D = -- (107-48 - 0-297 c). Cinchonidine hydrochloride, C 20 H 24 N 2 . H Cl + H 2 0. Solution in water, c = 1 to 3. (20) Salt [o] D = - (105-34- 076 c). (21) Alkaloid [o] D = - (123-98 - 1 05 c). Solutions in hydrochloric acid : 1 mol. hydrochloride + 2 mols. H 01 or 1 mol. alkaloid + 3 mols. H Cl + water to 100 cub. cent, c = 1 to 10. (22) Salt [o] D = - (154-07 - 1-39 c). (23) Alkaloid [a] D = - (181-32 -- 1-925 c). Cinchonidine sulphate (neutral), 2 (C 20 H 24 N 2 0) . H 2 S0 4 + 6H 2 0. (24) Solution in water, c = 1'06. Salt [o] D = 106-77. Alkaloid [a] D = - 142-31. Cinchonidine sulphate (mono-acid), (C^H^ N 2 0) . H 2 S 4 + 5 H 2 0. (25) Solution in water. c = 2. Salt [a] D = 110-5. Alkaloid [a] D = - 177'95. Cinchonidine disulphate (di-acid), (C^H^O) . 2H 2 S0 4 + 2H 2 0. Solution in water, c = 1 to 7. (26) Salt [a] D = - (105-96 -1-0267 c + 0-03376 c 2 -0'00104 c 3 ). (27) Alkaloid [a] D = - (185-77-3-1557 c + 0-18158 c 2 -0'00981 c 3 ). Quinidine or Conchinine (dextro-rotatory}. Quinidine hydrate, C 20 H 24 N 2 2 + 2 J H 2 0. Solution in alcohol of 97 per cent, by vol. c = 1 to 3. (28) Hydrate [a] D = +"(236'77 - 3-01 c). (29) Anhydride [a] D = + (269'57 - 3'90 c). Quinidine hydrochloride, C 20 H 24 N 2 2 . H Cl + H 2 0. Solution in water, c = 1 to 2. (30) Salt [a] D = + (205-83 - 4'93 c). (31) Alkaloid [a] D = + (240-45 - 6'60 c). Solutions in hydrochloric acid : 1 mol. hydrochloride + 2 mols. H Cl, or 1 mol. alkaloid + 3 mols. H Cl + water to 100 cub. cent, c = 1 to 5. 20'^ PRACTICAL APPLICATIONS OF ROTATORY POWER. (32) Salt [a] D = + (292-56 - 3'09 c). (33) Alkaloid [a] D = + (338 -37 - 4*52 e). Diquinidine sulphate, 2 C 20 H 24 N 2 2 . H 3 S 4 + 2 H 2 0. (34) Solution in water, c = 1. Salt. [a] D = + 179-54. Alkaloid [a] D = + 215'55. Solution in hydrochloric acid : 1 mol. salt -f 4 mols. II 01 + water. (35) Anhydrous salt, c = 2. [o] D = + 286'4. Alkaloid [a] D = 329'8. Solution in sulphuric acid : 1 mol. salt + 5 mols. H 2 S O 4 + water. (36) Anhydrous salt, c = 2. [a] D = + 281. Alkaloid [a] D = + 323. Quinidine sulphate, C 20 H 24 N 2 2 S O 4 + 4 H 2 0. Solution in water, c = 2 to 8. (37) Salt [a] D = + (212-0 - 0-8 c). (38) Alkaloid [a] D - + (323'23 - 1'86 c). Solution in sulphuric acid : 1 mol. disulphate + 2 mols. H 2 S 4 + water to 100 cub. cent, c = 1 to 10. (39) Sulphate [a] D = + (215-49 - 1-41 c). (40) Alkaloid [a] D = + (328-55 - 3'27 c). Cinchonine (dextro-rotatory) . Cinchonine, C 20 H 24 N 2 0. Solution in alcohol of 97 percent, by vol. c = 0'5. c = 1. Mean. (41) [a] D = + 226-36 225-96 226-13. Cinchonine hydrochloride, C 20 H 24 N 2 . H Cl + 2 H 2 0. Solution in water, c = 0*5 to 3. (42) Salt [o] D = + (165^50 - 2-425 c). (43) Alkaloid [a] D = + (204*46 - 37 c). Solutions in hydrochloric acid : 1 mol. hydrochloride + 2 mols. H Cl, or 1 mol. alkaloid + 3 mols. H Cl + water to 100 cub. cent, c = 1 to 7. (44) Hydrochloride [a] = + (214'0 - 172 c). (45) Alkaloid [o] D = + (264-37 - 2-625 c). Dicinchomne sulphate, 2 C 20 H 24 N 2 . H 2 S 4 + 2 H 2 0. Solution in water, c 1 to 2. (46) Salt [a] D = + (170-3 - 0-855 c). DETERMINATION OF CINCHONA ALKALOIDS. 203 (47) Alkaloid [o] D - + (20679 - 1-26 c). Solution in sulphuric acid : 2 mols. dicinchonine sulphate + 5 mols. H 2 S 4 + water to 100 cub. cent, or 3 mols. sulphuric acid to 1 inol. alkaloid, c = 0*5 to 6. (48) Sulphate [a] D = + (21910 - 1-85 c). (49) Alkaloids [o] D = + (266-07 - 2'69 c). For the rotatory powers of the other cinchona bases, see Chapter VII. 104. Oudemans 1 has determined the specific rotation [a] D of anhydrous quinine and cinchonidine (both laevo-rotatory) in solution in absolute alcohol for different degrees of concentration (c grammes of substance in 100 cubic centimetres), and at different temperatures t, with the following results : Quinine. t. c = 1. c = 2. c = 3. e= 4. c = 5. e= 6. 171-4 169-6 167-9 166-1 164-2 162-4 170-5 168-7 167-0 165-2 163-4 161-6 10 169-6 167-8 166-1 164-4 162-7 160-9 15 168-9 167-1 165-4 163-7 162-1 160-4 20 168-2 166-6 164-8 163-2 161-6 159-8 Cinchonidine. t. c = 1-5. c = 2. c = 2-5. c = 3. c = 3-5. c = 4. 15 110-0 109-6 109-2 108-8 108-4 108-0 20 109-0 108-6 108-2 107-8 107-4 107-0 By , employing a dilute alcohol as the solvent, the specific rotation of the cinchona alkaloids decreases with the amount of the dilution. 1 Oudemans: Lieblcf s Ann. 182, 46. The results obtained by Oudemans do not admit of strict comparison with those given by Hesse, as the former employed absolute, and the latter 97 per cent., alcohol. 204 PRACTICAL APPLICATIONS OF ROTATORY POWER. Oudemans gives the following observations on this point made at a temperature of 17 Cent. Quinine. Quinidine. Cinchonidine. Per cent. Per cent. Per cent. of Alcohol [<*] for of Alcohol []D for of Alcohol [o] D for by Weight. e = 1-62. by Weight. c = 1-62. by Weight. c - 1-54. 100-0 - 167-5 100-0 + 255-4 100-0 - 109-6 94-9 - 169-7 95-3 + 257-6 90-5 - 115-0 93-5 - 170-4 90-5 + 259-0 80-2 - 117-8 90-5 - 171-9 85-0 + 259-4 70-8 - 120-4 83-3 - 174-3 80-0 + 259-3 69-0 - 121-1 73-9 - 176-1 75-0 + 259-4 05-1 - 176-5 The following values, also given by Oudemans, for the specific rotation of the various salts, apply to solutions containing each 0*308 to 0*324 gramme (molecular weight of C 20 H 24 N 3 and C 20 H 24 N 2 2 ) of the particular alkaloid in 20 cubic centimetres of solution, or 1*54 to 1*62 grammes per 100 cubic centimetres. Temperature, 17 Cent. Salt. Solvent. Specific Rotation [a] D Anhydrous Salt. Alkaloid. Quinine Neutral Sulphate 2 (C 20 K, 4 N 2 2 ).H,S0 4 + 7 H 2 Acid Sulphate C 20 H 24 N 2 2 .H 2 S0 4 + 7 H 2 O Neutral Hydrochloride C 20 H 24 N 2 2 .HC1 + 2H 2 Neutral Oxalate 20 ' 2 + ziL, 6 Absolute Alcohol Water Absolute Alcohol Water Absolute Alcohol - 157-4 - 213-7 - 134-5 - 133-7 - 138-0 Absolute Alcohol - 13l'4 I - 214-9 - 278-1 - 227-6 - 163-6 - 169-0 - 160-5 DETERMINATION OF CINCHONA ALKALOIDS. 205 Specific Rotation [a] D . Salt. Solvent. Anhydrous Salt. Alkaloid. Cinchonidine Neutral Sulphate 2 (C 20 H 21 N 2 0)H 2 S0 4 + 6H 2 O Absolute Alcohol - 118-7 - 157-5 55 59 J5 Alcohol 89 per cent.by Weight - 128-7 - 171-8 95 55 59 Alcohol 80 per cent, by Weight - 131-2 - 175 1 Neutral Nitrate C 20 H 24 N 2 O.HNO 3 + H 2 Water - 99-9 - 126-3 59 55 59 Absolute Alcohol - 103-2 - 130-4 55 55 59 Alcohol 89 per cent.by Weight - 119-0 - 150-4 59 55 55 Alcohol 80 percent, by Weight - 127-0 - 160-4 Neutral Hydrochloride C 20 H 24 N 2 . H Cl + 2 H 2 Water - 104-6 - 129-2 59 55 55 Absolute Alcohol - 99-9 - 123-5 55 99 99 Alcohol 89 per cent, by Weight - 119-6 - 147-7 99 95 5' Alcohol 80 per cent, by Weight - 128-7 - 159-0 ConcMninc (Quinidinc) Neutral Sulphate 2 (C 20 H 21 N 2 2 ) .H 2 S0 4 + 2H 2 Absolute Alcohol + 211-5 + 255-2 Neutral Nitrate C 20 H 24 N 2 2 .HN0 3 Absolute Alcohol + 199-3 + 232-6 Neutral Hydrochloride C 20 H 24 N 2 O 2 . H Cl + 2 Ho Water + 190-8 + 233-6 55 Absolute Alcohol + 199-4 + 244-1 Alcohol 90-5 per cent, by Weight + 213-0 + 260-7 105. The constants given by Hesse and Oudemans serve for testing the purity of commercial samples. For this purpose it is necessary, of course, that the conditions in respect of solvent and concentration should be the same as in the determination of these normal values, and the temperature should not differ very much. Moreover, it is necessary, in dealing with compounds containing water of crystallization, to determine directly the amount of the latter, in order either to establish the identity of the same with the 206 PRACTICAL APPLICATIONS OF ROTATORY POWER. formula assigned, or, if it disagrees, to be able to find the per- centage of anhydrous substance, viz., of alkaloid present. To give some idea of the amount of variation that may be expected, a few determinations of specific rotations obtained by Hesse and Oudemans respectively, for the same substances are given below. This is only practicable in the experiments made on aqueous solutions, as the other solutions employed by these observers are not com- parable. Employing the constants given in 103, 104, the specific rotation for the pure alkaloid, in a solution of 1/6 grammes in 100 cubic centimetres, appears for the undermentioned salts as follows : Hesse. Oudemans. Difference. Quinine sulphate . . . . -,277 -278 1 Quinine hydrochloride . . . . - 160 - 164 4 Quinidine hydrochloride . . + 230 + 234 4 Quinidine hydrochloride . . - 122 - 129 7 It thus appears, that with samples equally pure, different observers may obtain values differing by seven degrees, or even more. The differences, however, which occur when impurities are present, are much larger in amount when another alkaloid is present, the specific rotations of the four cinchona bases differing very considerably from one another. This is shown in a number of experiments by Hesse, of which the results are as follows : A solu- tion of a specimen of neutral diquinine sulphate, which a separate analysis showed to contain 15 per cent, of water of crystallization was prepared with hydrochloric acid having a concentration c = 2 grammes anhydrous base. To prepare 50 cubic centimetres of this solution, since 85 parts of anhydrous base were equivalent to 100 parts of the hydrated substances, - -^ - =1*176 grammes, was oD required. This amount was put in a 50 cubic centimetre flask, together with so much standard hydrochloric acid to give for 1 mole- cule (C 20 H 24 . No 3 ) 2 . H 2 S 4 four molecules H Cl, and the resulting solution diluted up to the mark with water. Observed in a "Wild's polariscope with a 2 decimetre tube, the solution gave an angle of rotation a D = 9 '58, whence the specific rotation of the anhydrous 9-58 x 100 substance = - _ 239'5. A X A Now the figures in 103 (8), show that perfectly pure sulphate of quinine in such a solution gives [a] D = 239-2 (as a mean of three observations which gave respectively 239-1 ; 2391 ; DETERMINATION OF CINCHONA ALKALOIDS. 207 239 "3) and hence the preparation under examination must have been free from admixture. Three other samples of commercial sulphate of quinine, exa- mined under like conditions, gave the following specific rotations respectively : - 236-6, - 235-5, + 109-5. Of these the two first agree so nearly with the normal value that no admixture of foreign substance, at least in any appreciable quantity, could have been present ; the third, on the contrary, shows such a marked rotation to the right, that it must contain a notable amount of quinidine and cinchonine. In this way Hesse showed that a so-called quinidine disulphate of English houses is an essentially different product from pure quinidine (conchinine) sulphate as prepared by the firm of F. Jobst, of Stuttgart. These preparations exhibited the following differences : Quinidine (conchinine) sulphate, with 4 mols. HC1 c = 2 \ ri (anhydrous salt) I l English quinidine sulphate, with 4 mols. H Cl, c = 2 (anhy- I r -i __ 9r . drous salt) ) Quinidine (conchinine) sulphate, with 4 mols. H., S0 4 , c = 2 ) - _ (anhydrous salt) ......../ WD ~ English quinidine sulphate, with 4 mols. H S0 4 , = 2)-- ox^o (anhydrous salt) ...-..../ L a l-+W- The direct optical analysis of alkaloids in cinchona-bark extracts is, as Hesse remarks, beset with difficulty from the solutions contain- ing a yellow colouring matter, which cannot be removed alone, and which impedes accurate observation of rotation. Hence the polar- iscope cannot serve for the direct valuation of cinchona-barks, although it provides a useful check on the results obtained by other modes of analysis. 106. Optical Analysis of Mixtures of Cinchona Alkaloids. The quantitative composition of a mixture of two alkaloids may be deduced from its specific rotation with the aid of the values given in 103. To test this method Hesse 1 determined the specific rotations of a number of mixtures of known composition, to ascertain whether the former could be deduced from the rotatory powers of the constituents. This was found to be sufficiently exact, and there- 1 Hesse: Licbig's Ann. 182, 146. 208 PRACTICAL APPLICATIONS OF ROTATORY POWER. fore the association of alkaloids in solution does not materially interfere with, their individual optical properties. Hence a quantitative analysis by this method is practicable. 1 1 The mode of calculating the specific rotation of a mixture from those of its com- ponents will be best understood by taking an example. Let us suppose a mixture of 2 grammes of quinine hydrochloride with 1 gramme of cinchonine hydro - chloride dissolved in water to 100 cubic centimetres. The specific rotation of the separate salts is given by the formulae in 103 : For quinine hydrochloride (Form. 2) [o] D = - (144-98 - 3'15 c), And for cinchonine hydrochloride (Form. 42) [a] D = + (165-50 - 2-425 c). Whence for quinine hydrochloride, when c = 2 [a] D = - 138' 68, and for cinchonine hydrochloride when c = I [o] D - 163*07. Introducing these values for [a] in the equation - we obtain the angles of rotation a, which solutions of these strengths ought to give, when observed in a tube whose length I = 1 decimetre : For quinine hydrochloride when c = 2, angle a = - 2'774 ,, cinchonine hydrochloride when a, c = 1, ,, = + 1-631 For the mixture when c = 3, angle a = - M43. And hence the specific rotation of the mixture should be 1-143 x 100 _ - ]D ~ 1 x 3 Actual experiment gave for this solution [a] D = - 37-4, thus closely approximating to the calculated value. In dealing, however, with mixtures of unknown composition, we are unable to arrive at the true specific rotations corresponding to the amounts of the separate sub- stances present ; and we are forced to take for c in each case the total weight of mixture employed. But even so we obtain numbers closely agreeing with the results of actual experiment. Thus, suppose in the example given above we had taken c in each case as 3, and introduced into the equation the values for specific rotation corresponding thereto, viz : For quinine hydrochloride . c = 3. [a] D = - 135-53, ,, cinchonine hydrochloride c = 3. [a] D = + 158*23, we should have obtained from Quinine hydrochloride, c = 2. a = - 2*711 Cinchonine c = 1. a = + 1-582 Mixture c = 3. a ='- 1-129, as the angle of rotation for the mixture in a 1 decimetre tube, whence the specific rotation r -, M29 X 10 []= i x 3 - 376 ' This latter mode of calculation, although not strictly accurate, is found to yield fairly good results, so long as the 100 cubic centimetre mixture does not contain more than a few grammes of substance. In such cases the true values of c for the components do not differ greatly from the value of c for the whole mixture, and so the departure from the true specific rotations is small. DETERMINATION OF CINCHONA ALKALOIDS. 209 The mode in which the percentage composition of a mixture of two alkaloids is deduced from the observation of its specific rotation, will be seen from the following examples given by Hesse : I. Four grammes of a mixture of quinine hydrate and cincho- nidine were dissolved in alcohol of 97 per cent, by volume, to form 100 cubic centimetres of solution. Examined in a Wild's polar- iscope with a 2 decimetre tube, the solution gave an angle of rota- tion a D = 9*95, and thus the specific rotation of the mixture was The specific rotation of the individual alkaloids is, according to 103, when c = 4, Quinine hydrate, according to Form. (1) : [a] D = 142*57. Cinchonidine, according to Form. (19) : [o] D = 106'29. Putting x for the required percentage of quinine hydrate, whereby that of cinchonidine = 100 x, we get the equation -142-57* -106-29 (100-*) = 124-37 x 100, whence _ 100 (124-37 -106-29) 142-57 - 106-29 According to this, the mixture consists of Quinine hydrate 49 '8 parts. Cinchonidine 50 '2 100-0 parts. The real composition of the mixture actually consisted of equal parts of the alkaloids, with which the results of optical analysis coincide almost exactly. II. A mixture of 3 parts quinine sulphate and 1 part quinidine sulphate gave in an aqueous solution containing 4 grammes in 100 cubic centimetres, the specific rotation [a] D = 71*87 : > For quinine sulphate, according to Form. (9), when c 4 : [a] D = - 163*61. For quinidine sulphate, according to Form. (37), when c = 4 : [a] D = + 208*80. Indicating by x the percentage of quinine sulphate we have : - 163-61* + 208-80 (100 - x) =* 71*87 x 100; whence x 75*4 per cent. p 210 PRACTICAL APPLICATIONS OF ROTATORY POWER. Thus we have: By optical Actual analysis. composition. Quinine sulphate 75'4 75*0 Quinidine sulphate 24'6 25'0 100-0 100-0 III. A mixture of 1-714 grammes quinine and 1'756 grammes quinidine was dissolved in so much standard hydrochloric acid to give for 1 molecule of the two alkaloids (C 30 H 24 N 2 2 = 324), 3 molecules hydrochloric acid, and diluted with water to 100 cubic centimetres. This solution, of which the concentration c = 3'470, gave the specific rotation [a] D = + 27*92. In hydrochloric acid solution, when c = 3'47, the specific rota- tion is For quinine, according to Form. (5) :^ [a] D = 269-29. quinidine, (33) : [o] D = + 32373. Putting x for the proportion of quinidine, we have : 32373 x - 269-29 (100 - x] = 27'92 x 100. This gives x the values 50*1, the results appearing as hereunder : By optical analysis. Quinine 50'1 Quinidine 49 -9 Actual composition. 50-6 49-4 100-0 100-0 IY. 1-878 grammes of a mixture of quinidine (0'878 gramme) and cinchonine (1 gramme) made into a 100 cubic centimetre solution, containing 3 molecules hydrochloric acid for 1 molecule alkaloid (316), showed a specific rotation [a] D = + 291-80. With concentration c = 1'878, we have For quinidine, according to Form. (33) : [a]o = + 330-44. ., cinchonine (45) : [a] D = + 259'44. Putting x for the percentage of quinidine, we have 330-44 # + 259-44 (100 - x} = 291-80 x 100, DETERMINATION OF CINCHONA ALKALOIDS. 211 from which we have the following : By optical Actual analysis. composition. Quinidine 45'6 46'8 Cinchonine 54*4 53'2 100-0 100-0 To analyze a mixture of three cinchona alkaloids in a similar mariner, the specific rotation must be determined by means of two different solvents. Thus, Hesse 1 has investigated weighed mixtures of cinchonidine, quinidine, and cinchonine, in the following solutions : I. 0*5 gramme of the mixture dissolved in alcohol of 97 per cent, by volume, into a 25 cubic centimetre solution, so that the concentration c = 2 gave in a 2 decimetre tube an angle of rotation a = + 2-78, whence [o] D = + 69-5. II. 0-5 gramme of the same mixture dissolved in hydrochloric acid to a 25 cubic centimetre solution, containing 3 molecules H Cl to 1 molecule alkaloid, gave in a 2 decimetre tube a = -f 2 '82, whence [a] D = + 64'09. Now the specific rotations of the three alkaloids, with a concen- tration c = 2, are as follows : Solution in alcohol. Solution in hydrochloric acid. Cinchonidine [a] D = - 106*89 Form. (19) - 177'47 Form. (23) Quinidine [a] D = + 26177 (29) + 329'94 (33) Cinchonine [a] D = + 226*13 (41) + 259-12 (45) Putting x, y, z, for the several required proportions, cinchoni- dine = x, quinidine = y, and cinchonine = z, we get the equations : x + y + z = 100 - 106-89 x + 261-77 y + 226-13 z = 100 x 69-50 - 177-47 x + 329-94 y + 259-12 z = 100 x 64-09 From the solution of which we obtain : By optical Actual analysis. composition. Cinchonidine 51 '5 51 '3 Quinidine 42'9 38'3 Cinchonine 5-6 10-4 100-0 100-0 While the values for cinchonidine agree, there are considerable 1 Hesse: LieMg'* Ann. 182, 152. p 2 212 PRACTICAL APPLICATIONS OF ROTATORY POWER. differences between those for each of the other two alkaloids. These differences disappear when in the analysis of solution I. the angle of rotation 2'80 is substituted for 278, and in that of solution II. a = 2'80 instead of 2-82. Errors of observation thus exert considerable influence over the results, and, consequently, the optical analysis of a mixture of three alkaloids is attended with some uncertainty. 107. Other experiments for determining by the polariscope the composition of various mixtures of cinchona bases have been made by Oudemans, 1 jun., and with fairly satisfactory results. The following special method for determining the quinine in a mixture of quinine and cinchonidine, has been given by Oudemans: If to any solution (e. g., bark-extract) containing the above alkaloids, as sulphate or chloride, we add a solution of neutral tartrate of potash or Rochelle salt, the tartrates, being insoluble in water, are precipitated : Quinine tartrate (C^ H^ N 2 2 ) 2 . C 4 E 6 6 + H 2 0. Cinchonidine tartrate (C 30 H 24 N 2 0) a . C 4 H 6 6 + 2 H 2 0. Each of these compounds is readily soluble in dilute hydro- chloric acid, and Oudemans took the rotations in three solutions of different concentrations. Each of the solutions contained for every 0*4 gramme of the tartrates, 3 cubic centimetres normal hydro- chloric acid (containing 364 grammes H Cl per litre), and was made up with water to 20 cubic centimetres. At a temperature of 17 Cent, the following rotation-constants were observed : Quinine tartrate. Cinchonidine 0-4 grm. tartrate + 3 cub. cent. \ tartrate. normal hydrochloric acid / r _ r 1010 i L rl a ID = 215*8. o] D = 1313. -f water to 20 cub. cent- ( L solution 0'8 grm. tartrate + 6 cub. cent. \ normal hydrochloric acid / r J __ , , >| a | D = 211*o. |a] D = 129'u. + water to 20 cub. cent. ( L solution 1-2 grm. tartrate -f 9 cub. cent. \ normal hydrochloric acid / = _ ^ = _ L + water to 20 cub. cent. C L solution 1 Omlemans: J.iebiff's Ann. 182, 63, M. DETERMINATION OF CINCHONA ALKALOIDS. 213 By means of these figures the percentage composition may be determined of a mixture of the two tartrates, obtained as evaporated extract from a solution. For this purpose we dissolve 0'4, 0'8, or 1'2 gramme of the dried extract, in 3, 6, or 9 cubic centimetres normal hydrochloric acid, dilute the solution to 20 cubic centimetres with water, and observe the specific rotation at 17 Cent. Denoting this by M, and putting x for the required percentage of quinine tartrate, we can calculate its value from one of the following formulae : - 100 (M- 131-3) 215-8 - 131-3 100 (M - 129-6) 211-5 - 129-6 100 (M - 128-1) 207-8 - 128-1 ' A number of experiments by Oudemans showed, however, that the proportion of quinine calculated as above is, in most cases, too high. This is seen in the following results: Concentration 0'4 Concentration 0'8 Concentration 1'2 x = X X Tartrate of Observed Quinine calculated True P ercenta S e Concentration. Specific Rotation. from Specific of Tartrate of Rotation. Quinine. Difference. ( 152-5 25-1 per cent. 25-0 per cent. + o-i 165-7 40-7 39-7 + 1-0 0-4 183-5 61-8 60-0 + 1-8 195-3 75-7 75-2 + 0-5 ' ( 203-3 85-2 85-2 ( 150-2 170-8 25-0 per cent. 50-3 25-3 per cent. - 0-3 50-0 ,, + U-3 0-8 ) 183-7 66-0 64-3 ,, + 1-7 } 195-3 80-2 79-6 ,, + 0-6 I 195-1 80-0 80-2 - 0-2 1 147-5 24-3 per cent. 24-9 per cent. - 0-6 1-2 <^ 171-3 54-1 54-6 - 0-5 I 189-1 76-4 75-4 + 1-0 VII. ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 108. The following collection of rotation values embraces only such, substances as have been properly examined that is to say, those respecting which information has been recorded on the following points : l 1. Name of ray used (generally Dorj). 2. Nature of the solvent. 3. Concentration or percentage composition of solutions. 4. Temperature at which the angle of rotation has been observed. (In some cases this has been omitted through want of data.) 5. In the case of interpolation formulae, the limits within which they are correct. Accompanied with such data, specific rotation values, as marked in 40, afford, when the given experimental conditions are strictly observed, striking characters for the substances, useful in determining the nature of the substances as well as in examining the purity of particular samples. Moreover, they may serve other purposes, as follows : (a) For obtaining at least an approximate estimation of the percentage composition of solutions of active substance, in cases where the specific rotation of the substance does not alter very much with the concentration of its solutions. Thus given, the angle of rotation a of any solution in a tube 7 decimetre long, the number of 1 The list has no pretension to absolute completeness. Other substances which have been adequately examined may have escaped notice. DOTATION CONSTANTS OF ACTIVE SUBSTANCES. 215 grammes c of active substance per 100 cubic centimetres of solution may be found from the equation _ tt x 1QQ c ~ ["a] x l ' Similarly, the proportion of an active solid substance in ad- mixture with inactive substance can be found by dissolving a known weight, p, to a given volume, v cubic centimetres ; then the per- centage of solid substance present is represented by : a x v x 100 = [a] X / x p ' Of course, it is here assumed that the inactive ingredients present in solution exert no influence on the specific rotation of the active substance. (b) In certain cases also, for the quantitative analysis of mixtures of two active substances, as in .the case of the cinchona alkaloids, 106, 107. The values cannot, however, be applied in any way for comparison of the rotatory powers of different active substances with each other, as they refer only to solutions of a given composition^ and do not represent the actual specific rotation of the pure substance itself. All the specific rotations hereafter given, refer to the compounds of the exact composition denoted by the chemical formulas annexed ; so that, where the substance contains water of crystallization, the values refer to the hydrated substance. If the specific rotation of the anhydrous substance is required, it can be calculated from the formula [a] anhydrous = [a] hydrated, in which M represents the molecular weight of the hydrated substance, and m that of the anhydrous substance. As before : [a] D , [a]j denote respectively the specific rotation for ray D and for the transition tint/. a denotes angle of rotation for a layer 1 decimetre thick. c (concentration) the number of grammes of active substance in 100 cubic centimetres of solution. p ,, (percentage composition) the number of grammes of active substance in 100 grammes of solution. d ,, specific gravity of the solution. t temperature (Cent.) at which the rotation has been observed. 216 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. In referring to memoirs the following abbreviations have been adopted : L. A. stands for Liebig 's Annalen der Chemie u. Pharmacie. J. P. C. ,, Journal fur praktische Chemie. D. C. G. Berichte der deutschen chemischen Gesellschaft. R. Z. J. ,, Zeitschrift des Vereinsfur Rubenzwker Industrie des deutschen lieichs. A. C. P. ,, Annales de chiiiiie et de physique. C. R. ,, Comptes rendus. J. B. ,, Jahresbericht der Chemie. (Giesscii.) 109. Sugars, C 12 H 22 O n . Cane-Sugar, C 12 H 22 O n . Dextro-rotatory. Aqueous solu- tions. Tollens (D. C. Gr. 1877, 1403) gives the annexed formulae : 1. Specific gravity of solutions at 17 '5 Cent, referred to that of water of 4 Cent. Rotation observed at 20 Cent. p = 4 to 18. [o] D = 66-810 - 0-015553^ - 0-000052462 p*. p = 18 to 69. [a] D = 66-386 + G'015035^ - 0-0003986^. Q = 82 to 96. [a] D = 64'730 + 0-026045 q - 0-000052462 ? 2 . q = 31 to 82. [a] D = 63-904 + 0-064686 q - 0'0003986 q*. 2. Specific gravity of solutions at 17 "5 Cent, referred to that of water at 17 '5 Cent. Rotation at 20 Cent. p = 5 to 18. [a] D = 66-727 - 0-015534 p - 0-000052396 p 2 . p = 18 to 69. [o] D = 66-303 - 0'015016^ - 0-0003981 p 2 . Schmitz (D. C. G. 1877, 1414. E. Z. J. 1878, 48), from the experiments referred to in 37 gives the formulae : 1. Specific gravity of solutions at 20 Cent, referred to that of water at 4 Cent. Rotation observed at 20 Cent. q = 35 to 98. [a] D = 64-156 + C'051596 q - 0-00028052 q*. 2. Specific gravity of solutions at 20 Cent, referred to that of water at 17'5 Cent. Rotation at 20 Cent. c = 10 to 86. [o] D = 66-453 - 0*0012362 c - 0-00011704 c 2 . c = 3 to 28. [a] D = 66-639 - 0'020820 c + 0-00034603 c 2 . c = 3 to 28. [u] D = 66-541 - 0*0084153 c. Hesse (L. A. 176, 97) found for c = to 10. [a] u = 68-65 - 0'82S c + 0-115415 c- - 0-0054167 c 5 . ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 217 Previously, the following values of [a] D had been given, without taking into account the alterability of the rotation 1 : Observers. c W >^^jTFlr7r Arndtsen 77-394 67-02 A. C. P. (3) 54, 4o| ^9f+?* ,, . 4 " ' 47-276 67-33 A. C. P. (3) 54, 40^*^ <& 5, 33-891 66-86 A. C. P. (3) 54, 403 - \|^*?^ 4 Stefan . .... 33-762 66-37 Wiener Ak. 52, II. 4y6 ^5^V?J5 wild . ,: . , _.":- \./ 30-276 66-42 Polaristrob. Bern, 1865. Weiss . , J; .. _. 30-090 65-98 Wiener Ak. 69, III. 162. Tuchschmid . , .. 27-441 66-48 J. P. C. (2) 2, 235. Stefan . . 4 21-608 66-75 Ibid. Calderoii 19-971 67-08 C. R. 83, 393. Krecke . . . 16-470 67-02 Dissert. Utrecht. 1867. Girard and Luynes 16-350 67-31 C. R. 80, 1354. Weiss .... 14-570 66-04 Ibid. Stefan. . . 10-375 66-12 Ibid. Calderoii . . v 9-986 67-12 Ibid. Oudemans . 5.877 66-90 Pogg. Ann. 148, 350. The specific rotation for different ray >s has been determined, according toBroch's method, by Arndtsen (A. C. P. (3) 54, 403) and by Stefan (Sitz.-Ber. d. Wiener Akad. 52, II. 486). Arndtsen, employing solutions with 30 to 60 per cent, of sugar, obtained the following mean values: Lines C D E b F e [a] 53-41 67-07 85-41 88-56 101-38 126-33. Stefan, with solutions wherein p = 10 to 30 per cent., obtained as mean values : 43-32 b 87-88 S 47'56 F 101-18 C 52'70 G 131-96 D 66-41. H 157'06. can be derived from the equation V in ten-thousandths Lines A [a] 38-47 Lines E [a] 84-56 The latter values [a] = "p -- 5*58, taking the wave-length of a millimetre. 1 As the specific rotation observed by Girard and Luynes, and also by Calderon with sugar solutions, in which c = 10 to 20, viz., ([o] D = 67'1 to 67*3) differs consider- ably from 66-5, the result obtained by Tollens and Schmitz, Toll ens crystallized afresh some pure sugar, and examined the rotation in several crops (D. C.G., 1878, 1800). He obtained with c 10 the value [a] D = 66*48. (Specific gravity of the solutions at 1 7-5 Cent, with reference to that of water at 4 Cent.) The value 67 is certainly too h igh . 218 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. For the transition tint the following values have been obtained : p = 25. [a], = 72-92 . c = 10 to 20. [a] j = 73-20. Calderon (C. R. 83, 393). Adopting Montgolfier's ratio, a D : a d = 1 : 1'129, in the case of sugar ( 18, p. 43) we get, if [o] D = 66'5, [o]j = 75-08. With Weiss* co-efficient 1-034 ( 18), [oj = 68'76. Stefan's dispersion-formula gives for AJ = 5'5, [o]j 78*32. In alcoholic solutions, cane-sugar exhibits higher rotatory power than in aqueous solutions (R. Z. J. 1877, 803). Hesse (L. A. 176, 97) found that in solutions containing 50 per cent, of alcohol, with c = 5, and t = 15, [a] D = 66*70. No farther estimations were made. Sulphuric acid appears to increase the rotation. Hesse (L. A. 176, 97) employing the proportion : 1 mol. sugar (c = 6) to 1 mol. H 2 S 4 + water to 100 cubic centimetres with t = 15, obtained [o] D = 66-67. Alkalies diminish the specific rotation of cane-sugar. 1 mol. sugar + 1 mol. JNa 2 . c = 5 . t = 15. [o] D = 66'00. Hesse (L. A. 176, 97). According to Sostmann (R. Z. J. 1866, 272) the saccharimetric estimations of sugar in presence of alkalies, come out too low by the following amounts : Alkali. In solution of the concentration. Per 100 cubic centimetres solution c = 5 c = \Q 0=20 to 25 1 gramme potash (K 2 O) 0-426 0-650 0-915 1 ,, soda(Na 2 0) 0-450 0-907 1-217 Pellet (R. Z. J. 1877, 1036) gives the following values : c = 5-4 0=17-3 1 gramme caustic potash (K H) 0-170 0-500 1 ,, caustic soda (Na O H) 0-140 0-450 1 ,, ammonia 0-073 0-085 Lime causes a remarkable reduction of rotatory power. Miintz (R. Z. J. 1876, 737) records the following observations : Pure Sugar, c = 10. [a] = 67'0 With 0-409 gramme = mol. lime = 64-9 0-818 = = 61-3 1-637 = 1 = 56-9 3-274 = 2 = 51-8 ROTATION CONSTANTS OF ACTIVE SUBSTANCES, 219 Saccharimetric observations by the following observers* have shown that the addition of 1 part of lime destroys the rotatory power of i 0-64 part sugar according to Jodin (C. R. 58, 613). 0-79 1-12 1-22 1-25 0-90 1-00 Dubrunfaut. Bodenbender (R. Z. J. 1865, 167). Stammer (Dingier, P. J. 156, 40). Michaelis (Dingier, P. J. 124, 358). in solution with c = 6 -4 > Pellet c = 17'3 J (R. Z. J. 1877, 1036). The action of the lime is removed by neutralization with acetic acid. Baryta and strontia similarly diminish rotatory power : f part baryta destroys the rotation of 0-426 parts sugar, according to Bodenbender. 1 ,, ,, ,, ,, in 0-190 ,, when and obtained the results subjoined : Concentration of Solutions. c = 5. c = 10. c = 20. (5grm. [a] - 66-1 [o] = 66-2 [a] D = 66-3 10 65-3 65-3 65-6 on zu ,, 63-8 63-7 61-0 25 62-8 f 2-5 grm. 65-2 5 __ 63-8 63-8 Anhydrous 10 62-1 62-6 Soda. 15 60-4 59-8 .20 58-5 58-1 ( 0-5 grm. 65-9 1 64-7 65-0 2 62-7 63-5 Anhydrous 3 62-1 62-5 64-2 Borax. 4 ..v. 61-6 5 ,, 60-8 61-1 63-0 i 7 62-2 220 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. The presence of 1 gramme of each of the following salts was found to reduce the concentration of sugar solutions, as determined by the saccharimeter, by the respective amounts as below : Carbonate of potash '143 with c =10 \ Sostmann 0-185 c = 20 to 25 } (R. Z. J. 1866, 272). 0-044 c = 5-4 i PeUet 0-065 c = 17-3 / (R. Z. J. 1877, 1036). Carbonate of soda 0-093 ,, c = 10 0-254 c = 20 to 25 / Sostmann - 0-040 c = 5-4 ) 0-132 e = 17-3 J* Carbonate of ammonia 0'040 ,, c = 5 -4 . 0-067 c = 17-3 J Phosphate of ammonia 0-016 c = 5'4 \ p n (crystallized) 0-036 c = 17'3 J P ' Acetate of lead added in the proportion of 25 grammes to 100 cubic centimetres of sugar-solution produces no change in rotation. Miintz (R. Z. J. 1876, 737). Milk-sugar, C 12 H 22 O n + H 2 0. Dextro-rotatory. Freshly prepared aqueous solutions exhibit bi-rotation ( 27). Hesse obtained for constant rotation by heating the solutions (L. A. 176, 100) :- c = 2 to 12. t = 15. [o] D = 54 - 0-557 c + 0-05475 c" - 0-001774 c 3 . Alkalies reduce the specific rotation considerably. Acetyl-derivatives of milk-sugar. Schiitzenberger (L. A. 160, 91). (1) C 12 H 18 (C 2 H 3 O) 4 O n in water. c = 7'46. [o] D = 50-1. (2) C 12 H U (C 2 H 3 0) 8 O n in Alcohol, e = 2-18. [] = 32. c = 9-68. [o] D = 31. Minose. Trehalose, C 12 H 22 O n + 2 H 2 0. Dextro-rotatory. Aqueous solutions, after standing twenty-four hours, exhibit no change of rotatory power : Mycose. c = 10'03, [a], = 173'2. Mitscherlich (L.A. 106-17). Trehalose. e = 8'4 to 14 -8. t-= 15. [o]j = 199 (anhydrous 220) . Berthelot (A. C. P. [3] 55, 276). Melitose, C 12 H 22 O n + 3 H 2 0. Dextro-rotatory. Water, c = 17'27. t = 25. [a]j = 88 (anhydrous 102). Berthelot (A. C. P. [3] 46, 69). Melizitose, C 12 H 22 O n + H 2 0. Dextro-rotatory. Water, c = 1S'6 anhydrous substance, t = 20. [o]j = 94:1 (anhydrous), 89'4 hydrated. Berthelot (A. C. P. [3] 55, 284). Water, c not given. [<*] 88 -8 (hydrated). [o]j = P4- 8 (anhydrous). Villiers (A. C. P. [5] 12, 434). ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 221 110. Sugars, 6 H 12 O 6 . G-lucose. Dextrose, C 6 H 12 6 + H 2 0. Dextro-rotatory. Fresh solutions, prepared in the cold, exhibit bi-rotation ( 27). The following numbers refer to the reduced constant of rotation. The most accurate observations are those of Tollens ( 38), whence the following formulae are derived : For C 6 Hj 2 6 + H 2 0. Aqueous solution, t = 20. p= 8 to 91. [o] D = 47-925 + 0-015534 p + 0-0003883 p 2 . q = 9 to 92. [a] D = 53-362 - 0-093194 q + 0-0003883 ? 2 . For C 6 H 12 O 6 . p = 7 to 83. [a] D = 52-718 + 0-017087 p + 0-0004271 p~. q = 17 to 93. [o] D = 58-698 - 0-10251 q + 0-0004271 q 2 . Hoppe-Seyler (Mfd. chem. Untersuchungen L, 163) determined the specific rotation of diabetic sugar by Broch's method, employing a solution in which c = 36'277 anhydrous substance, and found : For rays C I) E b F [a] = 42-45 53-45 67'9 71'8 81-3 (?) In more recent investigations, Hoppe-Seyler (Fresenius, Zeitsch. fur anatyt. Chem. 14, 305), employing solutions of diabetic sugar with c = 14 to 29, obtained a mean value for [a] D = 56 '4 (anhydrous sub- stance). Hesse (L. A. 176, 102) has investigated the specific rotation of [a] D of various glucoses, and found, at t = 15, the following : Glucose - hydrate. Honey- sugar. Grape-sugar. Starch -sugar. Salicin- c sugar. 1 49-77 50-00 50-00 3 47-33 47-87 48-03 48-48 6 46-58 46-79 47-96 12 46-34 46-83 47-66 Anhydride 51-78 51-67 51-80 for c = 2-8 f or c = 3 for c = 2-5 These sugars are therefore identical with one another. Along with them must also be included amygdalin-sugar, which, with c = 2, 222 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. gave [a] D =49*25 (hydrate). On the other hand, phlorhizin- sugar (hydrate) showed a lower rotation, viz., with c = 3, [a] D 40 '9, and with c = 6, [a] D = 40-08. Another sample gave, with c = 8, [a] D = 39-9; and with c = 10-52, [o] D = 397. Hesse (L. A. 192, 174). For the transition tint [a]j, the following rotation values are recorded : 52, Bondonneau. 52*5, Clerget Listing. 53 2, Dubrun- faut. 55-1, Pasteur. 56, Berthelot. 57, Schmidt. 57'4, Bechamp. 577, Jodin. Lime reduces the rotatory power. A solution which contained, in 100 cubic centimetres, 0'98 gramme of lime for 6'9 grammes of grape-sugar, gave [a]j = 33'3. Jodin (C. E. 58, 613). Fruit-sugar. Lsevulose, C 6 H 12 6 . Lsevo- rotatory. The observations under this head are very incomplete, as the -effects of concentration have not been investigated. This substance exhibits a marked decrease of rotation with increase of temperature. For laevulose obtained from invert-sugar by the lime process, Dubrun- iaut (C. R. 42, 901) found the following values (c not recorded) : t 14 52 90 [a]j = - 106 - 79-5 - 53. When the temperature exceeds 90, a chemical change begins in the solutions. According to Neubauer (D. C. Gr. 1877, 829), at a temperature of 14, [o] D = - 100 (enot given). Jodin (C. R. 58, 613) gives the following values (t not given, 14?): Aqueous solution c = 12 '8. [o]j = - 104. Alcoholic ,, c = 12-8. [a], = - 92. Lime causes a considerable reduction of the rotatory power. A solution with c = 5, giving [o]j = 106, on the addition of 0'64 lime gave [a]j = 63. Jodin. Invert-sugar, C 6 H 12 6 . Lsevo-rotatory. The rotatory power decreases rapidly with increase of tempera- ture. Dubrunfaut (C. R. 42, 901) found for a solution, the strength of which is not stated : t 14 52 90 [a],= -26-65 13-33 Tuchschmid's observations (J. P. C. [2] 2, 235) show that an aqueous solution of invert-sugar with c = 17*21 has at Cent, a ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 223 specific rotation [a] D = 27'9, and that this value decreases with increase of temperature according to the formula [a]o = (27'9 0-32 t). According to which, at t = 87'2, rotation will be 0. Alcohol, according to Jodin (C. E. 58, 613), causes an important reduction in the laevo-rotation of invert-sugar, which can, moreover, by the application of heat, be converted into dextro-rotation. Lime also causes a decrease. According to Maumene (C. R. 80, 1139) different specimens of invert-sugar exhibit similar properties only when in their prepara- tion the proportions of water and acid, the temperature and duration of the action, and the mode of neutralization employed have been strictly identical. Galactose, C 6 H 12 6 . Dextro-rotatory. Exhibits bi-rotation. According to Fudakowski (Hoppe-Seyler's- Med. chem. Untersuchungen I., 164), it is a mixture of two different sugars of unequal rotatory powers. Sorbin, C 6 H 12 6 . Laevo-rotatory. Water, e = 23-9. [a], = - 46-9. Berthelot. Pelouze (A. C. P. [3] 35, 222). 111. Mannite Group. Mannite, C 6 H 14 6 . Pasteur (C. R. 77, 1192) and Bouchardat (C. E. 80, 120 ; A. C. P. [5] 6, 100) have shown that in aqueous- solutions (c = 15) with a tube-length of 3 to 4 metres, this substance gives a left-handed rotation of 0*1 to 0*3, whence [a]j = 0*03. Vignon (A. C. P. [5] 2, 433), also Miintz and Aubin (A. C. P. [5] 10, 533) consider mannite as inactive. The addition of various substances to aqueous solutions of mannite renders them optically active, dextro-rotatory in the case of boracic acid, borax, and borate of lime, and more feebly so with chloride and sulphate of sodium ; laevo-rotatory in the case of caustic potash, caustic soda, potassium carbonate, potassium, and hydrogen arsenate, lime, baryta, and magnesia. After saturation with acetic acid the solution either remains feebly laevo-rotatory or shows slight dextro- rotation. Sulphuric acid or acetic acid added even in large proportion to mannite solutions produces no activity (Bouchardat, Yignon, Miintz, and Aubin, loc. cit.). Certain derivatives of mannite are active, as, for example, nitro- mannite, diacetyl- and hexacetyl-mannite, which are dextro-rotatory, and mannite dichlorhydrin which is laevo-rotatory. 224 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. Mannitan is a variable mixture of dextro-rotatory and laevo- rotatory isomers, the proportions varying with the mode of produc- tion. (Bouchard at). The mannite obtained by the action of nascent hydrogen on inactive glucose, invert-sugar, dextrose, leevulose (from invert-sugar or inulin) is also inactive, as well as that from manna. But each of them becomes active on addition of borax or conversion into nitro- mannite (Miintz and Aubin). Nitro-mannite, C 6 K 8 (0 . N0 2 ) 6 . D xtro-rotatory. Ether. p = 4-2. [a], = 70'2. Krecke (Arch. Neerl. VII, 1872). Alcohol, p = 2. [a], = 63'7. ,, ,, ,, Alcohol, c = 7-5. [a] D = 40. Krusemann (D. C. G-. 1876, 1468). Treated with ammonium sulphide, nitro-mannite passes into inactive (?) mannite, which by the action of nitric acid becomes once more active. Loir (Bull. .we. chim. 1861, 113). Krecke, loc. cit. Duicite is inactive. Biot. Jaquelain (J. B. 1850, 536). The acetyl- derivatives of dulcite and dulcitan rotate feebly to the right. Bouchardat (A. C. P. [4], 27 ; 68, 145). Isodulcite, C 6 H 12 5 + H 2 0. Dextro-rotatory. Water, c = 10-2. [a], = 7'6. Hlasiwetz and Pfaundler (L. A. 127, 362). Quercite, C 6 H 12 5 . Dextro-rotatory. Water, c = 1 to 10. t = 16. [a] D = 24'3. Temperature without influence. Prunier (Bull. soc. chim. 28, 555, and C. R. 85, 808). 112. Carbo-hydrates, (0 6 H 10 O 5 ) n . The rotation data given by different observers for substances of this class differ so widely from each other, that they cannot be used as characteristic marks for the substances. Cellulose, dissolved in cadmium, or zincoxide-ammonia (ob- tained bv treating cellulose dissolved in cupric- oxide ammonia, with cadmium or zinc until a colourless solution is obtained) is inactive. Krecke (Arch. Neerl. VI. 1871). Collodion, according to Krecke, is inactive. According to Schiitzenberger (L. A. 160, 77) it is dextro- rotatory. Starch boiled for a few hours in water, solution of potash or of chloride of zinc, gives dextro-rotatory liquids. For p 2'22 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 225 to 3-88. [a]j = + 211. Starch solution heated with dilute sul- phuric acid at 100, gives first [a]j = 216, but the rotatory power quickly decreases with the formation of dextrin and dextrose. Bechamp (A. C. P. [3] 48, 458). Glycogen. Dextro-rotatory. Various modifications. [a]j = + 140 to 211. Tichanowitsch. Stscherbakoff ( J. B. 1870, 848). Imilin. Lsevo-rotatory. The data for dahlia- and elecampane- inulin, range from [a] 5 = 26 to 72. The inuloid of Popp (L. A. 156, 190), C 6 H 10 5 + H 3 O, with c = 2, gives [a]j = - 30-5. The rotatory powers of the acetic ethers of cellulose, starch, glycogen, and inulin have been determined by Schiitzenberger (L. A. 160, 74). Dextrin. Dextro-rotatory. The data range from [a]j = 139 to 213. Gum Arabic Acid. The varieties of gum arabic met with in commerce, are partly dextro-rotatory, and partly laevo-rotatory. Scheibler (D. C. Gr. 1873, 618) found, on examination of five samples in aqueous solution with c = 5, the specific rotations for [a] 5 = + 37*3 + 46-1 ; - 28-8; - 29'2 ; -30-0 respectively. On heating with dilute sulphuric acid, all these solutions become dextro-rotatory by the formation of gum-sugar (arabinose), C 6 H 12 6 . The gum of beet-root is, in general, dextro-rotatory, but at certain seasons and in individual plants it is found to be laevo- rotatory. Scheibler, loc. cit. Dextro-rotatory gum is further found in the stag-trufFel, and laevo-rotatory gum in couch-grass. Ludwig (J. B. 1869, 791 ; 1872, 8031. 113. Glucosides. Salicin, C 13 H 18 7 . Lsevo-rotatory. Water, c = 1 to 3. t = 15. [a] D = - (65-17 - 0'63 c). Hesse (L. A. 176, 116). Water, p = 2'78. [ojj = - 73-4. Biot and Pasteur (C. R. 34, 607). Populin, C 20 H 22 O 8 . Laevo-rotatory. Water, p = 1. [o]j = - 53. Biot and Pasteur, loc. cit. Phlorhizin, C 21 H 30 O n + 2 H 2 0. Laevo-rotatory. Alcohol of 97 per cent, (by vol.) c = 1 to 5. t - 22'5. [O]D = - (49-40 + 2-41 c). Hesse (L. A. 176, 117). Alcohol. p = 4-6. [] = - 52 1 Q d (L A 166 6Q) Wood Spirit, p - 3-9. [a] D = - 52 J 226 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 114. Derivatives of the Sugars. Besides the previously-mentioned nitric and acetic ethers, active amyl-alcohol and active lactic acid belong to this group. Active amyl-alcohol. Laevo-rotatory. Commercial fermentation. Amyl-alcohol gave, in a layer 1 decimetre deep, an angle of rotation [a] D = 1*97 (Le Bel) ; [o] D = - 276 (- 40 of Ventzke's scale for a length of 5 deci- metres. (Ley.) For the active amyl-alcohol obtained from the commercial product by separation as completely as possible from admixture with the inactive alcohol by Pasteur's or Le Bel's method, we have the following data : (a) Specimens obtained by Pasteur's method of fractional crystal- lization of amyl-sulphate of barium. Angle of Rotation for a Layer 1 decimetre in thickness. Specific Gravity. Specific Rotation Mo- Boiling Point. Observers. 1: a, = - 4 127tol28 Pasteur (C.R. 41, 296). 2 etj = - 3-4 128 Pedler (L.A.I 47, 245). 3 o D = - 3- 18 (46 divi- sions of Ventzke 1 for 1 Ley (D. C. G. 1873, 5 decimetres) 0-808 at 15. - 3-9 128 1365). 4 O D = - 1-4 to 1-6 (20 to 23 divisions of Ventzke for 5 Erlenmeyer and Hell decimetres) 0-812 at 19. - 1-8 127-5 (L. A. 160, 283). 5 O D = -0-92(8-5 divi- sions of Soleil for 2 Pierre and Puchot (C. decimetres) 0-825 at - 1-1 130 R. 76, 1332). (b) Amyl-alcohol, purified by Le Bel's method, by repeated treatment with hydrochloric acid gas, whereby the inactive portion is first converted into amyl-chloride and can then be removed by distilla- tion. Boiling-point, 127. 1 1 Ventzke [ray/] = 0-3457 angular degrees for ray D. 1 Soleil [ray/] = 0-2167 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 227 a D = 4*53 to 4'63 for 1 decimetre. (Specific gravity not given; but taking it as = 0'81, we get [a] D = 5'6 to 5'7.) Le Bel (Bull. soc. Mm. [2] 21, 542). . By repeated distillation with caustic potash, and still more quickly with metallic sodium, active amyl-alcohol is rendered inactive. Le Bel (Bull. soc. chim. [2] 25, 545). Lsevo- amyl-alcohol by repeated distillation with caustic soda becomes dextro-rotatory. a D = +2 for 1 decimetre according to Beignes Bakhoven (Pogg. Supp. Bd. 6, 329) ; but this is denied by Le Bel (Bull. soc. chim. [2] 25, 199) and Balbiano (D. C. GK 1876, 1692). According to Pierre and Puchot aqueous amyl-alcohol gives a stronger rotation than the anhydrous alcohol. Ley (D. C. Gr. 1873, 1370) is, however, unable to confirm this. DERIVATIVES OF ACTIVE AM YL- ALCOHOLS. Active valerianic acid. Dextro-rotatory. (a) From laevo-amyl-alcohol. Angle of Rotation for a Layer 1 decimetre in thickness. Specific Gravity. Specific Rotation []o. Boiling Point. Observers. 1 oj = 8-60 170 Pedler (L.A.I 47, 246). 2 o = 2-7 to 2-76 (39 to 40 divisions of Ventzke' s scale for 3 5 decimetres) a D = 3-37 (48-7 Ventzke for 5 decimetres) 0-933 at 19-5 + 3-6 168171 173 1 Erlenmeyer and Hell t (L. A. 160, 284, ) 293). 4 a D = 4-24 (61-2 Ventzke 5 decimetres x ... 0-917 at 15 + 4-6 173 ) 5 a D = 3-12 (45 Ventzke for 5 decimetres 0-917 at 15 + 3-4 174-175 ( Ley (D. C. G. 1873, ( 1368). 6 a D = 0-54 (5 Soleil for 2 decimetres) 0-947 at + 0-6 178 Pierre and Puchot (C. R. 76, 1332). Q 2 228 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. (b) From Leucin. a D = 1-18 for 1 decim. (17 divs. Ventzke for 5 decims.) Erlenmeyer and Hell (L. A. 160, 286). Valerianate of amyL Dextro-rotator) r . oj, = 7-6 for 1 decim. (44 divs. Ventzke for 2 decims.) d = 0-869 at 15. [o] D = 8'7. Boiling-point 186. Ley (D. C. G. 1873, 1369). u D = 4-3 for 1 decim. (40 divs. Soleil for 2 decims.) d = 0*874 at 0. [o] D = 4-9. Boiling-point 190. Pierre and Puchot (C. R. 76, 1332). a D = 2-3 for 1 decim. (33 to 34 divs. Ventzke for 5 decims.) Erlenmeyer and Hell. (L. A. 160, 289). The following derivatives from laevo-amyl-alcohol, giving an angle of rotation a D = 4' 63 for a length of 1 decimetre, have been prepared and examined by Le Bel (Bull. soc. ckim. [2] 21, 542) : Amyl-chloride (boiling-point 97 to 99). Dextro-rotatory. a = 1-10 for 1 decim. d = 0*886 at 15. [a] D = 1'24. Amyl-bromide (boiling-point 117 to 120). Dextro-rotatory. <* D = 4-60 for 1 decim. d = 1'225 at 15. [o] D = 3'75. Amyl-iodide (boiling-point 144 to 145). Dextro-rotatory. OD = 8-22 to 8-33 for 1 decim. d = 1'54 at 15. [a] D = 5'34 to 5'41. Methyl-amyl and amylene from active amyl-alcohol are inactive. (Le Bel.) The following other derivatives of amyl-alcohol and valerianic acid have been examined by Pierre and Puchot (C. R. 76, 1332) : Divs. Soleil a D for Sp. gr. Boiling-point. for 2 decims. 1 decim. at 0. [o] D Amyl aldehyde 92-5 +6 = 0-65 0-8209 + 0'8 Butyrate of amyl 170'3 8'5 = 0*92 0-8769 +1-05 Valerianate of butyl 173*4 3 = '0-325 0-8884 +0-4 propyl 157 9 = 0-975 0-8862 + 1-1 ,, ethyl 135-5 12-5 = 1-35 0*8860 + 1-5 ,, methyl 117*5 8*5 .'= 0-92 0-9005 + 1-0 The stability of the active amylic grouping is shown by the researches of Wurtz (L. A. 105, 295), in which amyl-iodide was con- verted into the cyanide (a red = 1'59 for a length of 1 decimetre), this into capronic acid (a red = 1'22), and this, again, by electrolysis, into di-amyl (a red = 3'20). Para-lactic acid. Active sarco-lactic acid. Dextro-rotatory. The investigations of Wislicenus (L. A. 167, 302) have shown that an ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 229 exact determination of the specific rotation of para-lactic acid is impossible as this substance, even at ordinary temperatures, passes gradually into the ether-anhydride, C 6 H 10 5 , and into lactide, C 3 H 4 2 , both of which are strongly laevo-rotatory. Freshly prepared, it shows in aqueous solutions, in which the degrees of concentration were determined by titration (reckoned as C 3 H 6 3 ) , the following specific rotation : c = 7'38 25-57 39-94 grammes. [o] D = + 2-7b 1-64 2-63 By standing, the rotation of the solutions gradually increases. If they be then diluted with water a sudden decrease of rotation takes place, which, however, gradually increases again, but without returning to its original amount. For example, two specimens of equal concentration gave the following results : Original solution c = 21'24. [o] D = + 1-41 [o] D = + 1'85 After keeping 1 month , 2'07 2-26 ,, 2 months ,, 3 Diluted with water c = 15- 75. after 1 month 2-21 2-45 2-66 2-64 1-99 2-13 2-29 2-41 The gradual increase here observed is due to the gradual con- version of the laevo-rotatory molecules of the anhydride, C 6 H 10 5 , originally present in the solution, into the dextro-rotatory molecules of the acid C 3 H 6 3 , which, moreover, is proved by the fact that, if we neutralize the liquid with alkali, it gradually recovers its acidity. The decrease of rotatory power on the adition of water, is explained by Wislicenus to be caused by the formation of the hydrate, C 3 H 6 3 + H 2 0, to which he assigns a rotatory power inferior to that of the acid itself. It requires but 2 or 3 per cent, of the anhydride to be present to give the solution of lactic acid distinct laevo-rotation. But in preparations that have been long kept the amount of rotation becomes considerable. Thus, a solution which had been kept in mcuo over sulphuric acid for a year and nine months, and whose com- position approximated very closely to 84 per cent. C 6 H 10 O 5 + 16 per cent. C 3 H 4 3 , gave in alcoholic solution with c = 19 '54, the specific rotation [a] D = 85 '9. Zinc para-lactate, Zn (C 3 H 5 3 ) 2 + 2 H 2 0. Lsevo-rotatory, The specific rotation in aqueous solution appears to increase with decrease of concentration. 230 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. Wislicenus (L. A. 167, 332) obtained the following results : Solution. Hydrated Salt. 1. c = 16-05. [a] D = - 6-36 11-01. 7-47. 6-83 13.' 7-41 5-45. 5-26. 7-34 7-60 Anhydrous Salt. 13-98. [o] D = - 7'30 9-60. 7-29 6-51. 7-83 5-36. 8-49 4-75. 8-43 4-58. 8-73 Solutions 1 and 2 were supersaturated. Para-lactate of lime, Ca (C 8 H 5 8 ) 8 + 9 H 3 0. Laevo -rotatory. Hydrated salt, Anhydrous ,, c = 7'23. c 5*35. [] D = - 3-87 [o] D = - 5*25 Wislicenus . 115. Vegetable Acids. Dextro-tartaric acid, C^Hg 6 . See 19, p. 47, Arndtsen. The formulae apply for q = 50 to 95 per cent. See also 26, p. 60, Krecke (For Influence of Temperature). Water c = 5 to 15. t = 15. [a] D = + (14-90 - 14 c} 1 Hesse t = 22-5. [a] D = + (15-22 - 0-14 c) J (L. A. 176, 129). c = 0-5 to 15. t = -20. [o] D = + (15-06 - 0-131 c} Landolt (D. C. G. 1873, 1073). The specific rotation of tartaric acid is considerably diminished by the presence of other acids. Biot (Mem. de I'Acad. 16, 229). Dextro-tartrates. Solutions in water. The following determinations (Landolt) are for the anhydrous salts. Temperature always at 20. K.H Na. H NH 4 .H Li.H Na 2 E b F G a 10-9 14-0 18-7 19*6 23-2 32'7 Australene. Distilled at 100 with reduced pressure. Portion I. [a]j = 24-3. Portion II. ' [a]j = 21'4. (Boiling-point, 161.) Berthelot (A. C. P. [3] 40, 5). (b) From Pinus sylvestris and P. Abies. Russian or so-called German oil of turpentine. [a], = 14-6 to 16-3. Luboldt. Australene from Pinus sylvestris, [a] D = 32*4. [a]j = 40'3 with t = 24-5, (a D = 277, d = 0'8547. Boiling-point, 155'5 to 156'5). Flawitzky (D. C. G. 1878, 1846). Australene from Swedish wood-tar of Pinus sylvestris, [a] D = 36'3 (d = 0-8631 at 16. Boiling-point, 156'5 to 157'5.) Atterberg (D. C. G. 1877, 1203). 234 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. II. Lsevo-rotatory turpentine oil. Terebenthene. (Neutralized aiid distilled.) (a) From Pinus Pinaster (P. maritima). French oil of turpen- tine. Commercial oils, a^ = - 18'2, Luboldt; a, = - 31*1, Gladstone; a - 35'4to36'5, Berthelot; 35'6, Gladstone; 36-5, Gernez; 40-0, Biot; 42-2, Mayer; 43'0, Deville; 43-4, Soubeiran and Capitaine ; 45-5, Buignet. For different rays, Wiedemann (A. P. 82, 222) found : Lines C D E b F G a = - 21-5 23-4 29'3 36'8 38'3 43-6 55'9 Terebenthene. [a]j = 42*3. (Distilled with reduced pressure, at temperatures bet ween 80 and 100. Boiling-point, 161.) Berthelot (A. C. P. [3] 40, 5). [a] D = -- 37-01 at 20 (d = 0*8629 at 20. Boiling-point, 161). Landolt ( 30, p. 66). [o] D = - 40*30 (d = 0-8685 at 10. Boiling-point, 156). Riban (A. C. P. [5] 6, 15). Iso-terebenthene. Obtained by exposing terebenthene for two hours to a temperature of 300. [o] D = - 9'45 (d = 0'8431 at 20. Boiling-point, 175). Riban (A. P. C. [5] 6, 218). (b) From P. Larix. Venetian oil of turpentine. [a], = - 6-0, Luboldt. [a], = - 5-24, Guibour 4 - and Bouchardat. (c) Templin oil. "Krummhoh" oil. 1. From the cones of Pinus picea. Crude : [a]j = -85'2. . [a]j = -98*8. Rectified: [a], = - 92-5. [a]j = - 107-6. Fluckiger, Berthelot (J. B. 1855, 643). 2. From young shoots of Pinus pumilio. 1 [a]j = - 8'2. Jolly, Buchner (L. A. 116, 328). By exposure to the air, turpentine oils experience a decrease of rotatory power by oxidation ( 30), whence probably these discrepan- cies in the data. When distilled, the unaltered and more highly rotatory portions are carried over first. For the alterations of the rotatory power of oil of turpentine at temperatures above boiling-point, see 16, p. 35. For information on the rotatory properties of the numerous derivatives of oil of turpentine, as they have been investigated by Deville (A. C. P. [2] 75, 37) and Berthelot (A. C. P. [3] 38, 38 ; 39, 10 ; 40, 5), reference must be made to the original memoirs. In the case of most of the solid substances examined the concentrations of 1 Pinus pwnilio is the dwarf pine (Krummholz) , a species with recumbent stem found in the Alps and Pyrenees. D.C.R. ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 235 the solutions employed have not been recorded. The complete data are given only for : Lcevo-rotatory camphene. Terecamphene, C 10 H 16 , obtained by heat- ing terebenthene-chlorhydrate with an alcoholic solution of potash or with stearate of soda. Biban (Bull. soc. chim. 24, 10) found for alcoholic solutions with q = 62 to 90 per cent, alcohol, at a tempera- ture of 13 to 14 : [o] D = - (53-80 - 0-03081 q). 117. Ethereal Oils. Commercial ethereal oils, being invariably mixtures of sub- stances often of opposite optical powers, exhibit so much diversity in respect of rotation values, that these are of no use as a test of their purity, and special data are accordingly worthless. 118. Resins. Euphorbone, C 15 H 24 (from euphorbia resin). Dextro- rotatory. Chloroform. c = 4. t = 15. [a] D = 18-8. Hesse (L. A. 192, 195). Ether. (d = 0-72). c = 4. t = 15. [o] D = 11-7. Podocarpic acid, C 17 H 22 3 . Dextro-rotatory. Alcohol, c = 4 to 9. [a] D = 136. - Ether. c = 4 to 7. [a] D = 130. Sodium salt, C 17 H 21 Na 3 -f 8 H 2 0. Oudemans Water. c = 4-6. [o] D = 82. f* (L. A. 166, 65) c = 6-4. [] = 79. c = 13-8. j>] D = 73. Alcohol of 93 per cent, e = 9 [o] D = 86. 119. Camphors. Laurel-camphor, C 10 H 16 0. Dextro-rotatory. For specific rotation in various solvents ( 36, p. 84). The following others have been obtained : Alcohol of 80 per cent, c = 2 6 10 [a] D = 40.9 39-25 38'65 [ Hesse Chloroform, c = 5. [a] D = 44'2 ) ( L - A - I76 > 119 )- Arndtsen (A. C. P. [3] 54, 418) has determined the specific rotation in alcoholic solutions for different rays, and with different 236 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. weight-percentages of alcohol (q). = 22-9. The formula hold for q = 50 to 95. [a] c = 38-549 - 0-0852 q [a] D = 51-945 - 0-0964 q [a], = 74-331 - 0-1343 q [a] b = 79-348 - 0-1451 q [a] F = 99-601 - 0-1912 q [a], = 149-696 - 0-2346 q Patchouli camphor, C 15 H 26 0. Laevo-rotatory. Fused. (t above 59). [a] D = -118.) Montgolfier In Alcohol. [o] D = - (124-5 + 0'21 c). j (Bull. soc. chim. 28, 414). Camphoric acid, from laurel-camphor, C 10 H 16 4 . Dextro- rotatory. Water c = 0'64. t = 20. [a] D = 46-2. Alcohol of 98 per f c = 2 '562. t = 20. [o] D = 47'5. cent, by weight. \c = 19-294. t = 20. [o] D = 47 '4. Acetic acid - c = 3-026. t = 20. [a] D = 46-3. 50 per cent. j c = 6-052. t = 20. [o] D = 46'2. by weight. ( c = 12-100. t = 21 -5. [o] D = 46-0. Landolt. Salts of dextro-camphoric acid. Solutions in water. Kj . C 10 H 14 O 4 c = 4 to 16. t = 20. [a] D = 14 '39 + 0'06 c. Na 2 . C 10 H 14 O 4 c = 2 ,, 9. t = 20. [a] D = 16-62 + 0'06 c. (NH 4 ) 2 .C 10 H M (V = 4 17. t = 20. [a] D = 16-98 + 0-13 c. Landolt. Methyl-camphoric acid, CH 3 . C 10 H 15 4 . Dextro-rotatory. Alcohol, p = 143.04. t = 19-3. [a} = 51-4. Loir (A. C. P. [3] 38, 485). For the rotatory power of other camphors and their derivatives no sufficient data exist. 120. Alkaloids. Conine, C 8 H 15 N. Dextro-rotatory. [o] D = 17-9. (d = 0-873 at 15. a D for 1 decimetre = 15-6). Schiff (L. A. 166, 94). [o] D = 10'6. (d = 0*846 ,, 12-5). Alcohol reduces specific rotation ; ether, benzene, and oil have no effect. Petit (D. C. G. 1877, 896). Nicotine, C 10 H 14 N 2 . Laevo-rotatory. (See 32, p. 72.) CINCHONA ALKALOIDS. Besides those already given, 103, 104, the following data have been further recorded, mostly by Hesse. 1 1 Numerous earlier observations on the rotatory powers of alkaloids were made by Bouchardat (Ann. chim phys. [3] 9, 213), Bouchardat andBoudet (Journ. de Pharm. et de Chim. [3] 23, 288), Buignet (Journ. de Pharm. et de Chim. [3] 40, 268), De Vrij and Alluard (Compt. rend. 59, 201). These data are for Biot's red ray ; but they are not now of much use, as the nature of solvent employed is scarcely ever recorded with sufficient exactitude. ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 237 [The alcoholic chloroform mixture, much used by Hesse as solvent, consists of one volume alcohol of 97 per cent, (by volume) with two volumes chloroform.] Quinine hydrate, C 20 H 24 N 2 2 -t- 3 H 2 0. Laevo-rotatory. Ether (d = 0-7296) c = 1-5 to 6. t = 15. [a] D = - (158-7 - 1-911 e). Alcohol of 97 per cent, (by vol.) e = I 10. t = 15. [a] D = - (145-2 - 0-657 c). 80 per cent. c = 1 6. t = 15. [o] D = - (165-81 - 8-203 c + 1-0654 c 2 - 0-04644 c 3 ). Alcoholic chloroform, c = 2. t 15. [o] D = - 141-0. c = 5. t = 15. [a] D = - 140-5. Hesse (L. A. 176, 206). Anhydrous quinine, C 20 H 24 N 2 2 . Laevo-rotatory. In absolute and aqueous alcohol. Oudemans, p. 203. Alcohol of 97 per cent, (by vol.) t = 15. c = 1. [o] D = - 170-5. c = 2. [o] D = - 169-25. Chloroform, t = 15. c = 2. [o] D = - 116-0. c = 5. [a] D = - 106'6. Hesse (L. A. 176, 208). Absolute alcohol, c = 1-64. t = 17. [a] D = - 167-5.^ Benzene. c = 0-61. t = 17. [o] D = - 136. Toluene. c = 0-39. t = 17. [a] D = - 127. ) Oudemans Chloroform. c = 1-465. t = 17. [] = - 117. | ( L - A - 182, 44). c = 0-775. t = 17. [a] D = - 126. J Quinine hydrochloride, C 20 H 24 N 2 O 2 . HOI 4- 2 H 2 0, Lsevo-rota- tory. Water (p. 199). Hydrochloric acid (p. 200). Absolute alcohol (p. 204). Alcohol of 97 per cent, (by vol.) c = 1 to 10. t = 15. [a] D = - (147'30 - 1-958 c + 0-1039 = - 138-75 223-2 225'7 223'6 213-9 209-5 Concentrated fuming acid. c = 2. [o] D = 158'8. Hesse (L. A. 176, 210). 238 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. Diquinine sulphate (neutral), 2 (C 20 H 24 N 2 2 ) . H 2 S 4 + 8 H 2 0. Lsevo-rotatory. Absolute alcohol (p. 200). Aqueous alcohol (p. 200). Alcoholic chloroform, e = 1 to 5. t - 15. [a] D = (157 '5 - 0-27 c). Hesse (L. A. 176, 213). Quinine sulphate (Mono-acid), C 20 H 24 N 2 2 . H 2 S 4 -f 7 H 2 0. Laevo-rotatory. Water (p. 200). Absolute alcohol (p. 204). Alcohol of 97 percent, (by vol.) c = 2. t = 15. [a] D = - 134-75. 80 ,, ,, c = 2. t = 15. [a] D = - 142-75. j Hesse (L. A. 60 c = 2. t = 15. [a] =-155-91. 176,215). Alcoholic chloroform. c 2. t = 15. [o] D = - 138-75. ' In alcoholic solutions with c = 2, the specific rotation decreases 0-65 for each 1 rise of temperature. Draper (Silliman''s American Journal] , [3] 11, 42). Quinine disulphate (di-acid), C 20 H 24 , N 2 3 . 2 H 2 S 4 + 4 H 2 0. Laevo-rotatory. "Water. c = 2 to 10. t = 15. [o] D = - (170-3 - 0-94 c}. Alcohol of 80 per cent, (by vol.) t = 15. c = 1. [o] D = - 154-5. 80 t = 15. c = 3. [o] D - - 153-3. Hesse (L. A. 176, 217). oxalate, 2 (C 20 H 24 N 2 2 ) . C 2 H 2 4 + 6 E 2 0. Laovo- rotatory. Absolute alcohol (p. 204). Alcoholic chloroform, c = 1 to 3. t = 15. [a] D = - (141-58 - 0'58 c}. Hesse (L. A. 176, 218). Cinchonidine, C 20 H 24 N 2 0. Laevo-rotatory. Alcohol 97 per cent, (by vol.) (p. 201). Absolute and aqueous alcohols (p. 205). Alcohol of 95 per cent, (by vol.) c = 2. t= 15. [a] D = - (113-53 - 0-426 c). 80 ,, ,, c = 2. t= 15. [a] D = - 119-5. Alcoholic chloroform c 2. = 15. [a] D = - 108-9. Chloroform e = 2. t = 15. [o] D = - 83'9. Hesse L. A. 176, 219). Absolute alcohol c = 1-54. t = 17. [o] D = - 109 -6. \ Oudemans Chloroform c = 1-545. t = 17. [o] D = - 77'3. } (L. A. 182, c=3-41. #=17. [a] D =- 74-0.) 44). Cinchonidine hydrochloride, C 20 H 24 N 2 . H Cl -f H 2 0. LEevo- rotatory. Water (p. 201). Hydrochloric acid (p. 201). Absolute alcohol (p. 205). Alcohol of 97 per cent, (by vol.) c - 3. t = 15. [a] D = - 108-0. Hesse 80 c =1. t = 15. [a] D - - 135-25. (L. A. 176, Anhydrous salt : Chloroform c = 2 - 85. t = 15. [a] D = - 24'2. j 920) ROTATION CONSTANTS OF ACTIVE SUBSTANCES. . 23t9 Dicinchonidine sulphate, 2 (C 20 H 24 N 3 0) . H 3 S 4 + 6 H 3 0. Laevo-rotatory. Water, c = 1-06. t = 15. [a] D = - IOG'8. Salt with 3 mols. water: alcohol of 80 per cent, (by vol.) c = 2. t = 15. [a] D = -144-5. Hesse (L. A. 176, 221). Cinchonidine sulphate, C 20 H 24 N 3 . H 3 S 4 + 5 H 2 0. Lasvo- rotatory. Water (p. 201). Alcohol of 80 per cent, (by vol.) c = 2. t = 15. [o] D = - 109-0. j Hesse (L. Alcoholic chloroform. c = 2. t = 15. [a] D = - lOl'O. / A. 176, 222). Cinchonidine nitrate (p. 205). Cinchonidine oxalate, 2 (C^ H 24 N 3 0). C 3 H 3 4 + 2 H 3 0. Lsaevo- rotatory. Alcoholic chloroform. = 1 to 3. t = 15. [o]s = - 98-7. Hesse (L. A. 176, 222). Quinidine (conchinine) hydrate, C 20 H 34 N 2 + 2 J H 2 0. Dextro-rotatory. Alcohol of 97 per cent, (by vol.) (p. 201). 80 ,, c = 2. t = 15. [a] = 232'7. Alcoholic chloroform c = 1. t = 15. [a] D = 244-5. c = 2. t = 15. [a] D = 241-75. Anhydrous alkaloid : Chloroform c = 1-756. t = 15. [a] D = 230-35. Hesse (L. A. 176, 223). Absolute alcohol (anhydrous alkaloid) : c = 1-62. t = 17. [a] D = 255'4. Benzene ,, ,, c = 1-62. t = 17. fajn = 195-2. Toluene ,, ,, c = 1'62. t = 17. [a] D = 200*6. Chloroform c = 1-62. t = 17. [o] D = 228'8. Oudemans (L. A. 182, 44). Quinidine hydrochloride, C 30 H 24 N 3 3 . H 01 + H 2 0. Dextro- rotatory. Water, hydrochloric acid (p. 201). Absolute alcohol (p. 205). Alcohol of 97 per cent, (by vol.) c = 2 to 5. t 15. [O]B = 212-0 - 2-56 c. ,, 80 ,, c = 2. t = 15. [o] D = 230-25. Acid salt: C 20 H 24 N 2 2 . 2 H Cl + H 2 0. Water, c = 2. t = 15. [a] D = 250-3. Hesse (L. A. 176, 225). Diquinidine sulphate, 2 C 30 H 24 N 3 2 . H 2 S0 4 + 2 H 2 0. Dextro- rotatory. Water. Sulphuric acid. Hydrochloric acid (p. 202). Alcohol of 80 per cent, (by vol.) c 2. t = 15. [o] D = 218*2. \ 60 c = 2. t = 15. [a] D = 227-0. / Alcoholic chloroform. c = 2. t 15. [a]b = 209-25. > Anhydrous salt : Chloroform. c = 3. [ n ] D = 184-2. i (L. A. 176, 226). >> c = 5. [a] D =' 180-1. ) 240 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. Quinidine sulphate, C 20 H 24 N 2 2 . H 2 S 4 4- 4 H 2 0. Dextro- rotatory. Water. Sulphuric acid (p. 202). Alcohol of 97 per cent, (by vol.) c = 2. t = 15. [a] D = 183. Hesse (L. A. 176, 227). Quinidine nitrate (p. 205). Quinidine oxqlate, 2 (C 20 H 24 N 2 2 ) . C 2 H 2 4 + H 2 0. Dextro- rotatory. Alcoholic chloroform, c = 1 to 3. t = 15. [a] D =189-0 - 2-18 e. Hesse (L. A. 176, 227). Cinchonine, C 20 H 2i N 2 0. Dextro-rotatory. Alcohol of 97 per cent, (by vol.) (p. 202). Alcoholic chloroform, c = 1 to 5. t = 15. [a] D = 238-8 - 1'46 c. Hesse (L. A. 176, 228). Absolute alcohol, c = 0-5 to 0'75. t = 17. [a] D = 223-3. ^ Chloroform. c = 0*455. t = 17. [a] D = 214-8. I Oudemans c = 0-535. t = 17. [a] D = 212-3. i (L. A. 182, 44). c = 0-560. t = 17. [a] D = 209-6. J Cinchonine hydrochloride, C 20 H 24 N 2 . H Cl + 2 H 2 0. Dextro- rotatory. Water. Hydrochloric acid fp. 202). Alcohol of 97 per cent, (by vol.) c = 1 to 10. t = 15. [o] D = 179-81 - 6-314 e + 0-8406 c 2 - 0-0371 r 5 . ,, 80 ,, c = 2. t = 15. [o] D = 188-9. 60 c = 2. t = 15. [a] D = 195-5. Alcoholic Chloroform c = 2. t = 15. [] = 152-0. Hesse (L. A. 176, 231). Dicinchonidine sulphate, 2 (C 20 H 24 N 2 0) . H s S 4 + 2 H 2 0. Dex- tro-rotatory. Water (202). Sulphuric acid (p. 203). Alcohol of 97 per cent, (by vol.) a = 3 to 10. / = 15. [o] D = 193-29 - 0-374 e. 80 ,, c = 2. * = 15. [o] D = 202-95 v Hesse 60 c = 2. *=16. [a] D = 204- 14 I (L.A.I 76, Alcoholic chloroform c = 2. < = 15. [o] D = 185*25 J 231). Cinchonine oxalate, 2 (C 20 H 24 N 2 0) . C 2 H 2 4 + 2 H 2 0. Dextro- rotatory. Alcoholic chloroform c = 1 to 3. t - 15. [a] D = 165-46 - 0'763 c. Hesse (L. A. 176, 232.) The changes in the specific rotation of quinine, cinchonine, conohinine and cinchonidipe in presence of different proportions of ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 241 hydrochloric, nitric, chloric, perchloric, formic, acetic, sulphuric, oxalic, and phosphoric acids have been investigated by Oudemans (L. A. 182, 51). Cinchotenine, C 18 H 20 N 2 3 + 3 H 2 0. Dextro-rotatory. Alcoholic chloroform, c = 2. t = 15. [o] D = 115'5. 1'mol. substance + 2 mols. H 2 S 4 + water, c = 2. t = 15. [a] D = 175-5. Hesse (L. A. 176, 233). Quinicine, C 20 H 24 N 2 O 2 . Dextro-rotatory. Chloroform, c = 2. t = 15. [o] D = 44-1. Hesse (L. A. 178, 260). Quinicine oxalate, 2 (C 20 H 24 N 2 2 ) . C 2 H 3 4 + 9 H 2 0. Dextro- rotatory. Alcoholic chloroform, c = 1 to 3. t = 15. [a] D = 20-68 - 1-14 c. Water. c = 2. t = 15. [a] D - 9-54. 1 mol. salt + 2 mols. H, S 4 + water, c = 2. t = 15. [a] D = 15'54. Hesse (L. A. 178, 261). Cinchonicine, C 20 H 24 N 2 O. Dextro-rotatory. Alcohol of 95 per cent, (by vol.) c = 1. = 15. [a] D = 48. Chloroform. c = 2. = 15. [o] D = 46-5. Hesse (L A. 178,262). Cinchonicine oxalate, 2 (C 2o H 24 N 2 0) . C 2 H 2 4 + 3 H 2 0. Dextro- rotatory. Alcohol of 97 per cent, (by vol.) c = 2. t = 15. [a] D = 23-5. \ Alcoholic chloroform. c = 1 to 3. t= 15. [a] D = 23'1. / Water. c = 2. t = 15. [a] D = 22-6. ( ' 26 3) Water + 2 mols. H 2 S O 4 . c = 2. t - 15. [a] D = 25'75. I Quinamine, C^ H 26 N 2 2 . Dextro-rotatory. Alcohol of 96 (?) per cent, (by vol.) c = 0-8378. [a> = 106-8. Hesse (L. A. 166, 272). Paytine, C 21 H 24 N 2 2 . Lsevo-rotatory. Alcohol of 96 (?) per cent, (by vol.) c = 0-4542. [o] D = 49'5. Hesse (L. A. 166, 272). Quinidamine (conchinamine), C 19 H 24 N 2 2 . Dextro-rotatory. Alcohol of 97 per cent, (by vol.) c = T8. t = 15. [a] D = 200. r -.t- Hesse (D. C. a. 1877, 2158). Geissospermine, C 19 H 24 N 2 3 . Laevo-rotatory. Alcohol of 97 per cent, (by vol.) c = 1-5. t = 15. [o] D = - 93'4. Hesse (D. C. G. 1877, 2164). Homocinchonidine, C 19 H 22 N 2 0. Lsevo-rotatory. Alcohol of 97 per cent, (by vol.) c = 2. t = 15. [o] D =- - 109-3. Hesse (D. C. G. 1877, 2156). 242 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. Cusconine, C 23 H 26 N 2 O 4 + 2 H 2 0. Laevo-rotatory. Ether (d = 0'72) e = \, t = 15. [a] D = - 27'1 \ c = 2. t = 15. [o] D = - 26-8 J Hesse Alcohol of 97 per cent, (by vol.) c = 2. t = 15. [a] D = - 543 I (L.A.I 85,303.) Water + 3 mols. H Cl c - = 0-5. t = 15. j>] D = - 71'8 ' Aricine, C 33 H 26 N 2 4 . Laovo'-rotatory. Ether (rf = 072) c = 1 to 2-5. * = lo. [a] D = - 94-7. Alcohol of 97 per cent, (by vol.) c = 1. t = 15. [a] D = - 54-1. Hesse (L. A. 185, 313.) Solution in hydrochloric acid gives no rotation. OPIUM ALKALOIDS. Morphine hydrate, 17 H 19 N 3 + H 2 0. Laevo-rotatory. Solutions in dilute soda. Hesse (L. A. 176, 190). 1 mol. alkaloid + 1 mol. Na 2 O. c = 2. t = 22-5. [o] D = - 67'5. 1 + 5 c = 2. t = 22-5. [a] D = - 70-2. 1 + 2 c = 5. t = 22-5. [a] D = - 71 -0. Morphine hydrochloride, 17 H 19 N 3 . H Cl + 3 H 2 0. Loovo- rotatory. Water, e = 1 to 4. t = 15. [o] D = - (100-67 - 1-14 c}. Water + 10 mols. H Cl. c = 2. t = 15 a . [a] D = - 94-3. Hesse (L. A. 176, 190). Morphine sulphate, 2 C 17 H 19 N 3 . H 2 S 4 + 5 II 2 0. rotatory. Water, c = I to 4. t = 15. [o] D = - (100-47 - 0-96 e). Hesse (L. A. 176, 190). Morphine acetate, C 17 H 19 N 3 . C 2 H 4 2 + 3 H 2 0. Lasvo- rotatory. Absolute alcohol. c = 1-2. fo] D = - 100-4. x Alcohol rf = 0-865. c = 0-97. [a] D = - 98'9. ) Oudemans Water. c = 2-5. [a] =- 77. ( (L. A. 166, 77). c = 0-996. [a] D = - 72. ^ Codeine, C 18 H 21 N 3 + H 2 0. Leovo-rotatory. Alcohol of 97 per cent, (by vol.) c = 2 to 8. t - 15. [o] D = - 135-8. 80 ,, c = 2. t = 15. [a] D = - 137-8. Chloroform c = 2. t = 15. [] = - 111-5. Hesse (L. A. 176, 191). Codeine hydrochloride, C 18 K 21 N 3 . H Cl + 2 F 2 0. La3vo- rotatory. Water. c = 2. t = 22-5. [a] D = - 108 "2. 1 mol. salt -I- 10 mols. H Cl + water, c = 2. t - 22-5. [o] D = - 105-2. Alcohol of 80 per cent, (by vol.) c = 2. t = 22-5. [a] = - 108. Hesse (loc, cit.) ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 243 Codeine sulphate, 2 18 H 21 N 3 . H 2 S 0^ + 5 H 3 0. Laavo- rotatory. wter - 2 Narcotine, C 22 H 25 N 7 . Laovo-rotatory. Alcohol of 97 per cent, (by vol.) c = 0'74. < = 22-5. [a] D = - 185-0. Alcoholic chloroform c = 2. t = 22-5. [a] D = - 191-5. Chloroform c = 2 to 5. * = 22-5. [ a ] D = - 2(>7'35. Hesse (L. A. 176, 192). Narcotim dissolved in hydrochloric acid. Dextro-rotatory. 1 mol. alkaloid + 2 mols. H 01 + water c = 2. [o] D = I- 47 0. 1 + 2 + c = 5. [a] D = + 46-4. 1 + 10 + c = 2. [a] D = + 50-0. 1 ,, + 2 ,, + alkaloid of 80 per cent, c = 2. [o] D = + 104-5. (by vol.) Hesse (L. A. 176, 193). Pseudomorphine hydro chloride, C 17 H 19 N 4 . H Cl + H 3 0. Laevo-rotatory. 1 mol. salt (c = 0-8 to 1'6) + 1 mol. H Cl + water, t = 22 -5 [o] D = - (114*76 - 4-96 c). 1 mol. salt (c = 2) + 5 mols. Na 2 O + water = 1 mol. 1 alkaloid + 5 mols. Na 2 O + 1 mol. Na Cl J * = 22 ' 5 \- a ^ = Hesse (L. A. 176, 195). Thebaine, C 19 H 21 N 3 O 3 . Las vo- rotatory. Alcohol of 97 per cent, (by vol.) c = 2. t = 15. [o] D = - 218-6 \ 97 c = 2. t = 25. [] = - 215-5 I Hesse 97 c = 1. t = 22-5. [a] D = - 216-4 j (L. A. 176,196). Chloroform c = 5. t = 22-5. [a] D = - 229-5 ' Thebaine hydrochloride, C 19 H 21 N0 3 H Cl + H 2 0. LaBvo-rotatory. Water, c = 2 to 4, * = 15. [a] D = - (168-32 - 2-33 c}. c = 2. t = 22-5. [a] D = - 163-25. 1 mol. salt + 10 mols. H Cl + water, c = 2. t = 22-5. [o] D = - 158-6 Hesso (L. A. 176, 197). Papaverine, C 21 H 21 N 4 . Laevo-rotatory. Alcohol of 97 per cent, (by vol). c = 2. t = 15. [o] D = - 4-0. Chloroform. c = 5. t = 15. [a] D = - 5-7. Hesse (L. A. 176, 198). Hydrochloride is inactive. Laudanine, C 20 H 25 N 4 . Laevo-rotatory. Chloroform. c = 2. t = 22-5. [a^ D = - 13-5. 1 mol. alkaloid (c = 1) + 2 mols. Na., + water. t = 22 -5. [a] D = - 11-4. Hesse (L. A. 176, 201). Hvdrochloride is inactive. R 2 244 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. Laudanosine, C 21 H 27 N0 4 . Dextro-rotatory. Alcohol of 97 per cent, (by vol.) c = 2-79. t = 15. [a] D = 103-2. 97 c = 2. t = 22-5. [a] n = 105-0. Chloroform. c = 2. t = 22-5. [a] D = 66'0. 1 mol. alkaloid (c = 2) + 2 mols. H Cl + water, t = 22-5. [O]D = 108-4. Hesse (L. A. 176, 202). Narceine, hydrocotarmne, crypiopine, meconine are inactive. STRYCHNINE ALKALOIDS. Strychnine, C 21 H 22 N 2 2 . Lasvo-rotatory. Alcohol, d = 0-865. c = 0'91. [o] D = - 128. \ Chloroform. c = 4. [] = - 130. j Oudeman8 s = 2-25. 03 = - 137 ' 7 - / a. c = 1-5. [] = - 140 Amyl alcohol. c = 0-53. [a] D = - 235 Brucine, C 23 H 26 N 2 4 . Lasvo-rotatory. Alcohol. c = 5-4. [oln = - 85. 121. Unclassified Vegetable Substances. Santonin, C 15 H 18 3 . Las vo- rotatory. Alcohol, c = 2. t = 20. 01 = - 230. Buignet (/. d. Pharm. et de chim. [3] 40, 252). This substance is characterized by very marked rotatory dispersion. Alcohol of 97 percent, (by vol.) c = 2. t - 15. [a] D = - 174-0. v 90 c = 2. t = 15. [a] D = - 175-4. Hesse (L. A. 80 c = 2. t = 15. [a] D - - 176-5. 176, 125). Chloroform. c = 2tolO. t = 15. [o] D = - 171-5. / Bichloro-santonin, C 15 H 16 C1 2 O 3 . Laevo-rotatory. Alcohol of 97 per cent, (by vol.) c = 1. t - 15. [o] D = - 23. Hesse (loc. cit). Santonic acid, 15 H 20 4 . Laevo-rotatory. Alcohol of 97 per cent, (by vol.) c = 1 to 3. t = 22-5. [o] D = - 25-8. ) Hesse 80 c = 2 3. t = 22-5. 0] = ~ 26 ' 5 - 1 ( loc - c *0- Santonate of soda, 2 (C 15 H 19 Na 4 ) + 7 H 2 0. Laevo-rotatory. Water, e = 2 to 6. t = 22-5. [a]* = - (18-70 + 0'33 o). The rotation decreases with increase of temperature. At 25, with c = 3 [o] D = - 20-0, and with c = 10 [a] = 21'7. Hesse (loc. cit). Picrotoxin, C 12 H 14 0^ Lsevo-rotatory. Alcohol, p - 3-125. 01 = - 28-1. Bouchardat and Boudet (/. Pharm. chim. [3] 23, 288). ROTATION CONSTANTS OF ACTIVE SUBSTANCES. 245 Echicerin, C 80 H^ 2 . Dextro-rotatory. Ether. d = 0*73. c = 2. t = 15. [a] D = 63'75. ) Jobst and Hesse (L. A. Chloroform. c = 2. * = 15. [a] D = 65'75. I 178, 49). Echitin, C 32 H 53 O 2 . Dextro-rotatory. Ether. e = 2. * = 15. [] D = 72-7. \ Jobgt and He sse (toe. *). Chloroform, c = 2. * = 15. [o] D = 7.5-3. ) Echitein, C 42 H^ 0. Dextro-rotatory. Ether. c = 2. * = 16. [a] D = 88. \ Jo bst and Hease (to. <) Chloroform, c = 2. * = 15. [o] D = 85-5 ) Echiretin, C 35 H 56 2 . Dextro-rotatory. Ether. c = 2. ^ = 15. [o] D = 54 -8. Jobst and Hesse (loc. cit). 122. Bile Constituents. Cholesterin, C 26 H^ 0, or C 25 H 42 0. Laevo- rotatory. From gall stones. Anhydrous substance. Ether. d = 0-72. c = 2. * = 15. [a] D = - 31-12. Chloroform. c = 2 to 8. * = 15. [a] D = - (36-61 + 0-249 c}. Hesse (L. A. 192, 178). Lindenmeyer (J. fur prakt. Chem. [1] 90, 323), examined by Brock's method solutions of cholesterin (with 1 mol. water?) in rock-oil, c = 10, and in ether, c = 7- 941, and obtained the follow- ing specific rotations : Lines B C D E b F G [o] = - 20-63 25-54 31-59 39-91 41'92 48*65 62'37. Phytosterin, C 26 H 44 0. Laevo-rotatory. From calabar beans or seed peas. Chloroform, c = 1-636. t = 15. [a] D = - 34-2. Hesse (L. A. 192, 177). The following determinations of specific rotation of bile acids were made by Hoppe-Seyler (J. fur prakt. Chem. [1], 89, 257) by Broch's method, employing sunlight. Glycocholic acid, C 26 H 43 N0 6 . Dextro-rotatory. From ox bile. Alcoholic solution, c = 9'504. The concentra- tion of the solution is without influence. Lines C D E b F G [a] = + 21-6 29-0 37'9 40-0 487 56'8. 246 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. Glycocholite of soda, C 26 H 42 Na N0 6 . Dextro-rotaUny. Alcohol, c 20-143. [a] D = 25 - 7. Concentration without influence. Water. c = 24-928. [a] D = 20-8. Taurocholate of soda, C 26 H 44 Na N S 7 . Dextro-rotatory. Alcohol, c = 9-898. [o] D = 24*5. [a] D = 39'0. Concentration without influence. Water. c = 8-853. [] D - 21-5. [a] D = 34-0. Cholalic acid, anhydrous, C 24 H^ 5 . Dextro-rotatory. From ox bile Alcohol, c = 3-338. [o] D = 50-2. From dogs' excrement Alcohol, c = 2.942. [a] D = 47'6. [a]j = 50'4. Cholalic acid, crystallized with water, C 24 H 40 5 + 2J H 2 0. Dextro-rotatory. From ox bile or dogs' excrement. Alcoholic solution, c = 2*962 (= 2 659 anhydrous substance). Lines E CD E b F G II Hydrated: [a] = 25-3 27'0 30-4 40-1 42'2 47*3 60'8 70-1 Anhydrous: [a] = 28-2 30-1 33'9 44'7 47'0 52'7 67'7 78'0 Other specimens of the crystallized compound gave the follow- ing rotations, calculated for the anhydrous acid : Alcohol, c = 4'43 anhydrous substance : [a] D = 34-8. ,. c 6-0695 ,, ,, L a > - 35 ' 4 - / f = 2-7065 ,, ,, [a]j = 35-2. \e = 2-0298 [a], = 34-5. (e = 1-8040 ,, ,, [4 = 34-2. Cholalate of potash, C 24 H 39 K O 5 . Dextro-rotatory. Solution in Alcohol, c 22. Lines CD E b F [a] = 23-7 30-8 38'5 40'9 47'5. Solution in water, c = 29'775. [o] D = 24-9. c - 22-332. [] D = 24-1. *~ 16-749. [] D m 24-6. c = 12-562. [] D = 25-9. c = 7-000. [ a ] D = 27-5. c = 6-004. [] D = 28-2. Cholalate of soda > C 24 H 39 Na0 3 . Dextro-rotatory. Alcohol, c = 2-2296. [a] D = 31 -4. Solution in water, c = 19-049. Lines BCD E IF [o] = 19-7 21-0 26-0 33-1 34-9 42-0. Decrease of concentration raises the specific rotation. ROTATION .CONSTANTS OF ACTIVE SUBSTANCES. 247 Cholalate of methyl, C 2i H 39 (0 H g ) 5 . Dextro-rotatory. Alcohol, e = 4-59. [o] D = 31'9. Cholalate of ethyl, C 24 H 39 (C s H 5 ) 5 . Dextro-rotatory. Solution in alcohol, e = 18-479. Lines S D E b [a] = 25-4 32-4 40'5 42-3. 123. Gelatinous Substances. All these substances, and particularly chondrin, possess strong laevo-rotatory powers. The following observations were all taken by de Bary (Hoppe-Seyler, Med. chem. Utttermchungen, 1, 71) : Glutin. Aqueous solutions. 1 - 6-12 /* = 24 to25 - Wi> = - 140<0 - ' \t = 35 to 40. [u] D = - 123-0. 2 .-3-06 {^ 24 to25 - WD= - 130 ' 5 - ' \ t = 35. [ a ] D = - 125-0. The rotatory power of glutin solutions decreases with rise of temperature. Concentration, on the other hand, has no important influence. The following experiments with aqueous solutions of concen- tration c = 3 P 06, show the effects of alkalies and acids : 1. Solution mixed with an equal vol. ammonia [o] D = - 130-5. 2. a few drops solution of soda [a] - 130'5. 3 an equal vol. soda [al D = - 112-5. 4. an equal vol. acetic acid [a] D = - 114-0. Chondrin. Pure aqueous solutions of sufficient transparency cannot be prepared, but the cloudiness disappears on the addition of a few drops of soda solution. For such a solution with c = 0'957, it was found that . .. ... . [a]j = 213'5. After the addition of an equal volume of soda solution . .; *:i ., . [a] 3 = 552'0. The latter solution diluted by the addi- tion of an equal volume of water . [a]j = 281'0. 124. Albumins. All the albumins are laevo-rotatory. The following observations on their specific rotation are given by Hoppe-Seyler (Zeitsch. fur . u. Pharm. 1864, 737). 248 ROTATION CONSTANTS OF ACTIVE SUBSTANCES. Serum-albumin. Neutral aqueous solution [o] D = - 56. Aqueous solution saturated with sodium chloride [o]s = - 64. Aqueous solution saturated with addition of acetic acid [a] D - 71. Aqueous solution with addition of concentrated hydrochloric acid till the precipitate at first formed again disappears [o] D = - 78 '7. Potash and soda solutions, by forming alkali-albumin ate, cause a considerable increase of rotatory power, even when present only in small quantity. Prolonged action of the alkalies, particularly at higher temperatures, again reduces the amount of rotation. Egg-albumin. Aqueous solution. Rotation independent of concentration [o] D = - 35 '5. Aqueous solution after addition of hydrochloric acid [a] D = - 37 '7. Casein. Dissolved in magnesium sulphate solution [o] D = - 80. Solution in dilute hydrochloric acid (4 cub. cent, of fuming acid per litre of water) [a] D = - 87. Solution in smallest possible quantity of soda solution [a] D = - 76. Albuminate (protein of Mulder), obtained by the action of con- centrated potash upon albumins, always exhibits higher rotatory power than the latter. The following maxima have been observed : Albuminate from serum-albumin [o] D = - 86. ,, uncoagulated egg-albumin [a] D = 47. ,, coagulated egg-albumin [a] D = - 58'5. ,, casein. Solution of casein in strong potash. Rotation varies with strength and amount of potash used [a] D = - 91. Paralbumin, from ovarian cysts. Examination of the natural feebly alkaline solutions gave in several observations : [o] D = - 59, - 61, - 64. Syntonin, obtained from myosin of muscles by solution in very dilute hydrochloric acid, or by the action of concentrated hydrochloric acid upon albumins (coagulated egg-albumin or fibrin). Solution in very dilute hydrochloric acid. Rotation independent of concentra- tion [a] D = 72. In weak alkaline solutions the substance exhibits very nearly the same amount of rotation. By heating the hydrochloric acid solutions in a closed vessel to, 100, the specific rotation rises to [a] = 84'8. APPENDIX. ON THE ESTIMATION OF MALTOSE AND DEXTRIN IN MALT WORTS AND BEERS. By J. STEINER, F.C.S. WHEN an infusion of malt in cold water reacts on soluble starch under certain definite conditions, a chemical change takes place, which has attracted the attention of chemists for a considerable time. This chemical reaction being, moreover, of great practical importance in brewing, for example, numerous experiments have been performed to explain it. The results arrived at, although differing widely in many respects, lead nevertheless to the conclusion, that the starch is converted by the action of cold malt extract (diastase) into maltose and dextriris. These compounds are the only products under the most favourable conditions of temperature (55 to 63 C.), if the diastatic action continues no longer than two to three hours. But a more prolonged contact of the diastase leads to the partial con- version of maltose into dextrose, while the gradual saccharification of some of the dextrins into maltose, and the formation of dextrins of simpler molecular compositions seem to proceed during the whole time of the diastatic action. If starch be boiled with dilute sulphuric or hydrochloric acid, dextrins, maltose, and finally dextrose are produced, but if the action be too protracted, or the acid too concentrated, the so-called neutral carbo-hydrates are formed simultaneously. These latter are not capable of fermentation, nor of reducing alkaline solution of metallic salts, and have no rotatory power. The progress of the conversion may be watched by an iodine solution, which gives the following colour reactions. First, a deep-blue (soluble starch) ; secondly, a violet (amylo-dextrin) ; thirdly, a red (erythro-dextrin) ; and finally, no change of colour (achro-dextrin, maltose and dextrose.) 250 APPENDIX. All these substances possess a rotatory power, and in the following lines an account will be given of some experiments carried out for the purpose of ascertaining whether the optical properties of a malt wort, or beer, can be used for the determination of the relative proportions of maltose and dextrin contained in such solutions. But having to deal with a mixture, another characteristic property of these carbo-hydrates, ?'.5 14-76 grms. 1-014 3-6 grms. 1-0388 15*7 grms. 1-0472 12-5 grms. Before inversion. H || si II Jl |1 s 13 8 1 fel 83 So ^ II il 83 As Maltose. As Maltose. As Maltose. As Maltose. As Maltose. As Maltose. grms. 14.24 13-24 11-65 per cent. 71-56 66-53 55-54 grms. 13-7 12-9 per cent. 71-92 66-86 grms. 9-936 9-517 8-247 per cent. 67-36 64-50 65-91 grms. 1-89 1-758 1-713 per cent. 52-5 48-83 47-53 grmp. 10-75 10-61 0-67 per cent. 68'51 67-58 6i-eo grms. 8-90 fc-50 7-90 per cent. 7f20 68-00 6320 Sachsse's Knapp's Angle of rotation OD * - 429 31-5:7 I 33-36 27-3 After inversion . . - (13-91 gr. t dextrose 13-4 gr. dextrose. ' - 14 gr. dextrose. ll-4gr. dextrose. A comparison of these numbers shows, firstly, that the composi- tion of a strong, or first wort (I. to III.), differs from that obtained during sparging (IV.) ; and secondly, that even if the cupric oxide reducing power of a boiled wort (VI.) closely agrees with that of an unboiled wort (I.), it must not, therefore, be concluded that their respective deportments towards Knapp's and Sachsse's will be alike. These data are too few to permit of any general conclusion with regard to the nature of the different dextrins in worts ; but it appears that the dextrins in samples I. to III. possess a similar reducing power. The properties of maltose are [a] D = 138'5 (for a concentration of 10 grammes per 100 cubic centimetres), and a cupric oxide reduc- ing power R F = 61 per cent, dextrose (for a 1 per cent, solution, and if the test liquor is not diluted). Supposing, then, the dextrins in I. to III. have a specific rotation [a] D = 120, and a reducing power R F = 37 per cent, dextrose (or R s = 35 per cent., and R K = 21 per cent.), 100 grammes of extract would contain : In Sample III,, 42 per cent, dextrin + 42 per cent, maltose. In Sample II., 34'6 per cent. + 47'96 per cent. Whether these are the exact proportions of maltose and dextrin in such worts can only be proved by further investigations. The following polariscope observations serve as an additional APPENDIX, 255 proof that the composition of a first or concentrated malt wort differs from a wort obtained after sparging : -Three samples of wort from the same brew of specific gravities M050, 1-0483 (II.), and 1-0201 (V.), were collected at intervals from the taps of the mash tun. Part of the concentrated wort (specific gravity, 1'105) was diluted to 1-0489 (I.), and the rest to 1-0217 (IV.).* A sample of the same brew, after boiling with hops, of specific gravity 1-062, was diluted to specific gravity 1D493. (III.) The amounts used for observation were carefully measured with a 50 cubic centimetre pipette, and after the addition of 2 cubic centimetres basic acetate of lead, made up to 100 arid 110 cubic centimetres respectively. Conditions of Sample. Specific gravity. Angle of rotation O D corresponding to 100 cub. cent, of solution. I. Concentrated wort diluted . II. Sample direct from mash tun III. Boiled wort 1-0489 1-0483 1-0493 27-68 28-23 28-03 IV. Concentrated wort .... V. Sample direct from mash tun 1-0217 1-0201 12-06 13-05 The worts procured after sparging have therefore a greater rotatory power than the concentrated first wort. (C) The beer resulting from the worts referred to under (A) and (B) was subsequently analyzed, on the eleventh day from the date of mashing (100 cubic centimetres contained 47 grammes extract). 250 cubic centimetres of this beer were treated with about 3 cubic centi- metres basic acetate of lead, diluted to 500 cubic centimetres, and filtered. Beers act on Knapp's test much more violently before clarification than after, and it is therefore necessary to clarify for analysis. The final reaction of the mercury tests is in this case more precise than that of Fehling's, the working of which may, however, be rendered less difficult if to 50 cubic centimetres Fehling's, 200 cubic centimetres water are added, i.e., if the test liquor is diluted four times. The following results were obtained : (i.) Angle of rotation, a D = 10*17. (ii.) Fehling's, Sachsse's, and Knapp's solutions were reduced thus : Fehling's = 39 cub. cent., therefore 39 : -414 : : 500 : (x = 5-308 gr.) or 2-123 gr. maltose in 100 cub. cent. beer. Sachsse's = 42-5 cub. cent., therefore 42'5 : '5097 : : 500 : (x = 6'00 gr.) or 2*40 gr. maltose in 100 cub. cent. beer. Knapp's = 38-5 cub. cent,, therefore 38-5 : -3134 : : 500 : (as = 5-50 gr.) or 2-20 gr. maltose in 100 cub. cent. beer. 256 APPENDIX. (iii.) 50 cubic centimetres of the diluted beer were inverted with. 5 cubic centimetres acid for five and a half hours, and made up to 100 cubic centimetres. 50 cubic centimetres Fehling's required 24'9 cubic centimetres ; therefore 24-9 : -253 : : 100 : (x = 1-016) or 4-064 gr. dextrose in 100 cub. cent. In the analyses above, it appears that Fehling's gives the lowest and Sachsse's the highest result, and the same is noticeable in other samples of beer, the analyses of which are given in the table below. Sample. Extract per 100 cc. I. 4-8 grammes. II. 4'1 grammes. III. 3-2 grammes. IV. 4'7 grammes. Before inversion .... O CD rQ -^ CD <0 rQ fel 1 o h . O CD ij II Ij As Maltose. As Maltose. As Maltose. As Maltose. Fehling . grms. 1-808 1-998 1-880 per cent. 37-7 41-6 39-4 grms. 1-23 1-50 1-453 per cent. 30-0 36-6 35-4 grms. 0-80 1-185 1-052 per cent. 25-0 37-0 32-9 grms. 2-123 2-400 2-200 per cent. 45-17 51-06 46-81 Sachsse Knapp Angle of rotation a . . 11-52 10-73 7-6 10-17 After inversion .... ( 4-05 grms. \ dextrose. 3.85 grms. dextrose. ? 4-06 grms. dextrose. These results seem to indicate, not only that the dextrin in beer has a reducing power, but also that this dextrin differs in its pro- perties from those in worts. Supposing the dextrin in beer to have a specific rotation of MD = 131, and a cupric oxide reducing power R F = 3 per cent, dextrose, the composition would be of Sample IV., 1-72 grammes dextrin + 2'03 grammes maltose per 100 cubic centimetres. Sample II., 243 + Ml Sample I, 2'02 +1-71 These latter calculations are made merely for an illustration, but the actual proportions of maltose and dextrin in beers and worts remain still to be proved. APPENDIX. 257 Before concluding these lines, the analyses of a few samples of starch-sugars are given to illustrate that the results of Fehling's, Knapp's, and Sachsse's solutions differ also in this instance, but in a different ratio from that of worts or beers. In the analysis below Sachsse's solution gives the lowest and Fehling's the highest result. Sample. I. II. III. IV. y Fehling's. . . . Sachsse's .... Knapp's .... Sugar before inversion (as dextrose). per cent. 75-93 65-72 72-52 per cent. 78 63 70-41 72-85 per cent. 76-00 ' 66-67 71-81 per cent. 71-52 69-60 70-91 per cent. 62-00 55-31 p Angle of rotation a D 10 gr. in 100 cc. 11-42 9-48 9-b4 10-93 10-60 Sugar after inversion (as dextrose). All three solutions. 89-70 86-05 82-83 81-50 83-26 Naturally the explanation of the results of starch-sugar analyses is still more difficult, on account of the presence of maltose and dex- trose, besides dextrins, all three of which are formed by the mineral acid used in their production. A general comparison of the results given in this paper shows that : 1st. In the analysis of worts Fehling's and Sachsse's tests lead to results which differ only little, and are much higher than those cor- responding to Knapp's. 2nd. In testing beers Fehling's solution is reduced least and Sachsse's most, and it remains to be proved whether the higher results of the mercury tests are not partly due to the presence of the albuminous matter, which cannot be removed by lead acetate. 3rd. Solutions of starch sugars have the greatest action on Fehling's test, but least on Sachsse's, the numbers for the latter being in this instance even surpassed by those of Knapp's test. The subject of these lines requires careful consideration, and I intend carrying on further investigations in order to elucidate the various points which here have only been touched upon. INDEX. Formula for calculating, 50 Acid : Arabic, 225 Aspartic, 27, 232 Camphoric, 29, 236 Cholalic, 246 Dextro-tartaric, 230 Grlutamic, 232 Glutanic, 232 Glycocholic, 245 Lsevo-tartaric, 231 Malic, 27, 231 Para-lactic, 228 Podocarpic, 235 Quinic, 233 Santonic, 244 Valerianic, 227 Vegetable, 230 Acids : Rotation influence of, 35 a D : Relation of, to a,., 46 Albuminate, 248 Albumins, 247 Egg, 248 Serum, 248 Alcohol : Amyl, 28, 226 Alkaloids, 236 Cinchona, 198, 236 Analyzer, 4 Angle : Critical, 8 [note] Aricine, 242 Asparagin, 27, 232 Australone, 233 B Beers : Estimation of maltose and dextrin in, 249 Bile : Constituents of, 245 Biot : Experiments of, 64 Bi-rotation : Phenomenon of, 61, 197 Broch : Process of, 124 Brucine, 244 C Camphor : Laurel, 235 Patchouli, 236 True specific rotation of, 88 Carbo-hydrates, 224 Carbon : Asymmetrical, 24, 26, 29, 31 Casein, 248 Cellulose, 224 Chemical constitution : Dependence of optical activity on, 24 Cholesterin, 245 Cinchona bases : Determination of, 198, 236 'Optical analysis of mixture of, 209 Cinchonicine, 241 Oxalate, 241 Cinchonidine, 201, 238 Disulphate, 201, 239 Hydrochloride, 201, 238 Nifcrate, 239 Oxalate, 239 Sulphate, 201, 239 Rotation constants of, 198, 203 INDEX. 209 Cinchonine, 202, 240 Hydrochloride, 202, 240 Disulphate, 202, 240 Oxalate, 240 Cinchotenine, 241 Clerget : Inversion method of, 187 Codeine. 242 Hydrochloride, 242 Sulphate, 243 Concentration .- Calculation of, 162 Conchinamine, 241 Conchinine, 205 Conine, 236 Cornu : Instrument of, 117 Corrections : Schmitz' table of, 163 Crystals : Active structure of, 19 Cusconine, 242 Degrees : Veiitzke, 169 Angular measurement, 169 Dextrin : Estimation of, 249 Specific rotation of, 250 Dextro- gyrate, 8 Dextro-rotatory, 8 Diabetometers, 193 Dispersion : Formulae of, 43 Rotatory, 43 E Echicerin, 245 Echiretin, 245 Echitein, 245 Echitin, 245 Errors : Correction of, 169 Euphorbone, 235 F Folding : Solution of, 25,1 Filtration : Alteration during, 134 Flasks : Graduated, 144 Standardizing of, 145, 183 Fringes: Parallel, 110 G Galactose, 223 Geissospermine, 241 Glucose: Determination of, 190 Glucose anhydride : True specific rotation of, 90 Glucose hydrate : True specific rotation of, 90 Glutin, 247 Glycogen, 225 Gravity, specific : Details of calculation of, 142 Determination of, 138 H Hesse : Observations of, 55, 198 Researches of, 209 I Homocinchonidine, 241 Impurities: Removal of optically active, 187 Removal by filtration, 134 Instruments, vide Polariscopes. Inulin, 225 Knapp : Solution of, 251 Laavo- gyrate, 8 Las vo- rotatory, 8 Laevulose, 222 Lamp : For instrument, 102 For sodium flame, 99 Lang : Process of, 125 Laudanine, 243 i Laudanosine, 244 Laurent : Polariscope of, 118 Le Bel : Hypothesis of, 24 260 INDEX. Light : Ordinary, 1 Polarized, 1 Polarized by reflection, 1 Polarized by refraction, 3 Vertical band of, 100 Liquids : Constitution of active, 20 Specific gravity of, 138 M Maltose : Estimation of, 249 Mannitan, 224 Mannite, 223 Group, 223 Melitose, 220 Melizitose, 220 Method: Inversion, 187 Micose, 220 Milk sugar : Determination of, 197 Rotatory power of, 197 Mitscherlich : Polari scope of, 98 Molecules : Asymmetrical structure of, 21 Optically different modification of, 21 Morphine, 242 Acetate, 242 Hydrochloride, 242 Sulphate, 242 N Narcotine, 243 Nicotine, 72, 236 Nitro-mannite, 224 O Observation : Method of double, 171 Oils : Ethereal, 235 Kruramholz,234 Templin, 234 Oudemans: Investigations of. 55, 203 Papaverine, 243 Para-albumin, 248 Paytine, 241 Phlorhizin, 225 Phytoeterin, 245 Picrotoxin, 244 Plane : Impassable, 9 [note] Potarimeter : Rotation, 98 [note] Polarimetre, 98 [note] Polariscope : Cornu's, 117 Jellett's, 117 Laurent's, 118 Actual observations by, 120 Construction of, 119 Mode of observation with, 121 Mitscherlich' s- : Construction of, 98 Lamp for, 99 Larger form of, 104 Mode of observation with, 102 Wild's: Construction of, 108 Mode of observation with, 110 Observations by, 115 With saccharimetric scale, 176 With Savart's prism, 108 Polariscopes : Comparison of, 122 Polaristrobometer, 98 [note] Polarization : By reflection, 1 By refraction, 3 Circular, 8 Theory of, 19 Note on, 8 Plane of, 2, 5 Polarizer, 4 Populin, 225 Precipitates : Error due to, 1 84 Prism : Nicol's, 3 Construction of, 8 [note] Savart's, 107 Pseudomorphine : Hydrochloride, 243 Pycnometer : Sprengel's, 139 Method of filling, 140 Specific gravity by, 141 Q Quercite, 224 Quinamine, 241 Quinicine, 241 Oxalate, 241 INDEX. 261 Quinidamine, 241 Quinidine : Rotation constant of, 198, 203 Hydrate, 201, 239 Hydrochloride, 201, 239 . Nitrate, 240 Oxalate, 240 Sulphate, 202, 240 Quinine : Rotation constant of, 108, 203 Anhydrous, 203, 237 Estimation of, when mixed with cin- chonidine, 212 Hydrate, 237 ;-: Hydrochloride, 199, 237 Oxalate, 238 Sulphate, 200, 238 R Radicles active, 24 Ray : Determination of angles for different, 124 Extraordinary, 3 Linear polarized, I Transverse section of, 1 Reducing power (cupric oxide) : Of malt extract, 251 Of starch-sugars, 257 Reducing power (mercuric oxide) : Of malt extract, 251 Of starch-sugars, 257 Reducing powers (cupric and mercuric oxides) : Comparisons of, 252, 253, 254, 255, 256, 257 Reflection : Polarization by, 1 Total, 4, 8 [note] Refraction : Polarization by, 3 Refractive indices, 8 Representations, graphical, 68, 71, 76, 80, 86 Resins, 235 Resorcin, 30 Right-rotating, 8 Rotation : Magnetic, 18 Molecular, 93 Relative directions of, 113, 114 Specific, 49 Calculation of law of, 55 Data necessary for determining, 95 Rotation, specific: Dependent on amount and nature of solvent, 53 Dependent on thickness of medium, 42 Dependent on wave length, 43 Determination of true, 64 Influence of observation-errors on, 148 Influence of temperature on, 51 Influence on, by acids, 35 Influence on, by alkalies, 35 Influence on, by salts, 35 Method of determining, 83 Practical application of, 154 Theories as to cause of variation of, 62 Values, worthlessness of, 92 Variability of, in solution, 53 Rotatory power : Nature of, 16 Of malt extract, 251 Of starch- sugars, 257 Qualitative examination of, 98 S Saccharimeter : Soleil-Duboscq, 174 Scale of, 175 Soleil- Ventzke-Scheibler, 1 5 5 Construction of, 155 Correction of readings for, 163 External form of, 159 Mode of observation with, 160 "With angular graduation, 178 Saccharimetry : Optical, 154 Salicin, 225 Santonin, 244 Scale : Soleil-Duboscq, 175 Ventzke, 162 Schmitz : Tables of, 1 6 j, 180 Solution : Fehling's, 251 Knapp's, 251 Preparation of, 133 Process of clearing, 186 Sachsse's, 251 Solutions : Decolorization of, 186 Sorbin, 223 Spar : Iceland, 3 Spiral, lead, 130 262 INDEX. Sprengel: Pycnometer of, 139 Starch, 224 Starch- sugars : Estimation of, 257 Strychnine, 244 Substances : Active, 10 Artificial production of, 31 Classification of, 10 Derivatives of, 11 Rotation constants of, 214 Rotatory power of derivatives of, 35 Simultaneous influence of, 59 Gelatinous, 247 Inactive, 8 Inactivity of artificial, 32 Vegetable, 244 Sugar : Calculation of percentage of, 178 Derivatives of, 226 Detection of, in urine, 194 Detection of, in wine, 195 Estimation of, in urine, 194 Fruit, 222 Invert, 222 Of formula C^.,0^ 221 Of formula C 12 Ho 2 O H , 216 Tartaric acid, 21 Abnormal rotatory dispersion of, 47 Tartrate of ethyl : Specific rotation of, 77 Temperature : Arrangement for constant, 110 Influence of, 172 I Terebenthene, 234 ! Terecamphene, 235 Terpenes, 233 Thickness : Standard of, for solids and liquids, 42 Tint : Transition, 103 Trehalose, 220 Tubes: Adjustment of, 128 Measurement of lengths of, 128, 130 Turpentine : Right-handed oil of, 70 Specific rotation of, 66 U Urines: Diabetic, estimation of, 1 94 Van'tHoff: Theory of, 24 W Water bath, 129 Wave lengths, 125 Weighings: Reduction of, to vacuo, 135 Wine: Chaptalized, 195 Worts : Reducing power of, 253 Rotatory power of, 253 I'nrdon and Sons, jt'riiittra, L'al'-nwsttr Row, London. With Illustrations, 8^0., price 21s. Studies on Fermentation : THE DISEASES OF BEER, THEIR CA USES AND THE MEANS OF PREVENTING THEM. By L. PASTEUR, Member of the Institute of France, the Royal Society of London, &c. A Translation, made with the Author's sanction, of " Etudes sur la Biere," with Notes, Index, and original Illustrations, by FRANK FAULKNER, Author of the "Art of Brewing," &c., and D. CONSTABLE ROBB, B.A., late Scholar of Worcester College, Oxford. 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THE LIFE AND COMPLETE WORKS OF BENJAMIN THOMPSON, COUNT RUMFORD. With Notices of his Daughter. By GEORGE ELLIS. With Portrait. Five Vols. 8vo. 4/. 145-. 6d. Schorlemmer. A MANUAL OF THE CHEMTSTRY OF THECARBON COMPOUNDS OR ORGANIC CHEMISTRY. By C. SCHORLEMMER, F.R.S., Lecturer in Organic Chemistry in Owens College, Manchester. 8vo. 14?. "// appears to us to be as complete a manual of the metamorphoses of carbon as could be at present produced, and it must prove eminently useful to the chemical student." Athenaeum. B i8 SCIENTIFIC CATALOGUE. Shann. AN ELEMENTARY TREATISE ON HEAT, IN RELATION TO STEAM AND THE STEAM ENGINE. By G. SHANN, M.A. With Illustrations. Crown 8vo. 4*. 6d. Smith. HISTORIA FILICUM : An Exposition of the Nature, Number, and Organography of Ferns, and Review of the Prin- ciples upon which Genera are founded, and the Systems of Classifi- cation of the principal Authors, with a new General Arrangement, &c. By J. SMITH. A.L.S., ex-Curator of the Royal Botanic Garden, Kew. With Thirty Lithographic Plates by W. H. FITCH, F.L.S. Crown 8vo. 12s. 6d. " No one anxious to work up a thorough knowledge of ferns can afford to do without it" Gardener's Chronicle. South Kensington Science Lectures. Vol. I. Containing Lectures by Captain ABNEY, F.RS., Professor STOKES, Professor KENNEDY, F. J. BRAMWELL, F.R.S., Pro- fessor G. FORBES, H. C. SORBY, F.R.S., J. T. BOTTOMLEY, F.R.S.E., S. H. VINES, B.Sc., and Professor CAREY FOSTER. Crown 8vo. 6s. [Vol. II. nearly ready. Vol. II. Containing Lectures by W. SPOTTISWOODE, P.R.S., Prof. FORBES, H. W. CHISHOLM, Prof. T. F. PIGOT, W. FROUDE, F.R.S., Dr. SIEMENS, Prof. BARRETT, Dr. BURDEN-SANDER- SON, Dr. LAUDER BRUNTON, F.R.S., Prof. MCLEOD, Prof. ROSCOE, F.R.S., &c. Crown 8vo. 6s. SpOttis WOO de. POLARIZATION OF LIGHT. By W. SPOTTISWOODE, President of the Royal Society. With numerous Illustrations. Second Edition. Cr. 8vo. 3^. 6d. (Nature Series.) " The illustrations are exceedingly well adapted to assist in making the text comprehensible" Athenaeum. "A clear, trustworthy manual" Standard. Stewart (B.X Works by BALFOUR STEWART, F.R.S.,[Professor of Natural Philosophy in Owens College, Manchester : LESSONS IN ELEMENTARY PHYSICS. With numerous Illustrations and Chromolithos of the Spectra of the Sun, Stars, and Nebulae. New Edition. Fcap. 8vo. 4*. 6d. The Educational Times calls this the beau-ideal of a scientific text- book, clear, accurate, and thorough" PRIMER OF PHYSICS. With Illustrations. New Edition, with Questions. iSmo. is. Stewart and Tait. THE UNSEEN UNIVERSE: or, Physical Speculations on a Future State. By BALFOUR STEWART, F.R.S., and P. G. TAIT, M.A. Sixth Edition. Crown 8vo. 6^. " The book is one which well deserves the attention of thoughtfal and religious readers. . . . It is a perfectly sobtr inquiry, on scientific grounds, into the possibilities of a future existence." Guardian. PHYSICAL SCIENCE. 19 Stone. ELEMENTARY LESSONS ON SOUND. By Dr. W. H. STONE, Lecturer on Physics at St. Thomas' Hospital. With Illustrations. Fcap. Svo. 3.$-. 6d. Tait. LECTURES ON SOME RECENT ADVANCES IN PHYSICAL SCIENCE. By P. G. TAIT, M.A., Professor of Philosophy in the University of Edinburgh. Second edition, revised and enlarged, with the Lecture on Force delivered before the British Association. Crown Svo. gs. Tanner. FIRST PRINCIPLES OF AGRICULTURE. By HENRY TANNER, F.C.S., Professor of Agricultural Science, University College, Aberystwith, Examiner in the Principles of Agriculture under the Government Department of Science. i8mo. is. Taylor. SOUND AND MUSIC : A Non-Mathematical Trea- tise on the Physical Constitution of Musical Sounds and Harmony, including the Chief Acoustical Discoveries of Professor Helm- holtz. By SEDLEY TAYLOR, M.A., late Fellow of Trinity Col. ledge, Cambridge. Large crown Svo. 8s. 6d. " In no previous scientific treatise do we remember so exhaustive and so richly illustrated a description of forms of vibration and of wave-moti n in fluids" Musical Standard. Thomson. Works by SIR WYVILLE THOMSON, K.C.B., F.R.S. THE DEPTHS OF THE SEA : An Account of the General Results of the Dredging Cruises of H.M.SS. "Porcupine" and " Lightning " during the Summers of 1868-69 and 70, under the scientific direction of Dr. Carpenter, F.R.S., J. Gwyn Jeffreys, F.R.S., and Sir Wyville Thomson, F.R.S. With nearly 100 Illustrations and 8 coloured Maps and Plans. Second Edition. Royal Svo. cloth, gilt. ^is. 6d. The Athenaeum says : ' ' The book is full of interesting matter, and is written by a master of the art of popular exposition. It is excellently illustrated, both coloured maps and woodcuts possessing high merit. Those who have already become interested in dredging operations will of course make a point of reading this work ; those who wish to be pleasantly introduced to the subject, and rightly to appreciate the news which arrives from time to time from the ' Challenger? should not fail to seek instruction from it" THE VOYAGE OF THE "CHALLENGER." THE ATLAN- TIC. A Preliminary account of the Exploring Voyages of H.M.S. "Challenger," during the year 1873 and the early part of 1876. With numerous Illustrations, Coloured Maps & Charts, & Portrait ofthe Author, engraved'byC. H.JEENS. 2 Vols. Medium Svo. 42*. The Times says : " // is right that the public should have some attthoritative account of the general results of the expedition, ana B 2 20 SCIENTIFIC CATALOGUE. Thomson continued. that as many of the ascertained data as may be accepted with con- fidence should speedily find their place in the general body of scientific knowledge. No one can be more competent than the accomplished scientific chief of the expedition to satisfy the public in this respect. . . . The paper, printing, and especially the numerous illustrations, are of the highest quality. . . . We have rarely, if ever, seen more beautiful specimens of wood engraving than abound in this work. . . . Sir Wyvilie Thomsons style is particularly attractive ; he is easy and graceful, but vigorous and exceedingly happy in the choice of language, and throughout the work there are touches which show that science has not banished sentiment from his bosom." Thudichum and Dupre. A TREATISE ON THE ORIGIN, NATURE, AND VARIETIES OF WINE. Being a Complete Manual of Viticulture and QEnology. By J. L. W. THUDICHUM, M.D., and AUGUST DUPRE, Ph.D., Lecturer on Chemistry at Westminster Hospital. Medium 8vo. cloth gilt. 25.5-. tf A treatise almost unique for its usefulness either to the wine-grower, the vendor, or the consumer of wine. The analyses of wine are the most complete we have yet seen, exhibiting at a glance the constituent principles of nearly all the wines kn