30
THE JOURNAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
and have the finished fluids contain the same percentage of alcohol. Variations in the amount of moisture and extractive in the drug, and slight variations in conditions and amount of alcohol lost, all tend to cause considerable variation in the alcohol content of the resulting fluid extracts. Hence, in order to make a fluid extract contain a standard content of alcohol, i t is necessary t o assay i t for alcohol and finally adjust it t o the standard by the removal or addition of alcohol. It is also advisable t o assay the fluid extract again after it has been adjusted, for the adjusting of a large lot of fluid extract to within I per cent. of alcohol is not a n easy matter and considerable variations are liable t o occur. With this fact in view, the question naturally arises, how accurately can pharmaceutical preparations be assayed for alcohol? ’ I n making alcohol assays there are several sources of error: I. I n Measuring the Sample.-An error of 0.25 cc. on a 25 cc sample means t h a t a 90 per cent. alcohol will test 89 per cent. and a 50 per cent. alcohol only 49.5 per cent. An error of 0 .I cc. in measuring the sample means t h a t a 90 per cent. alcohol will test 89.6 per cent. and 50 per cent. alcohol 49.8 per cent. Then there is another similar error in adjusting the distillate to the definite volume required for taking the specific gravity. 2. Loss of Alcohol o n Distillation.-There seems t o be a slight loss of alcohol on distillation, due perhaps t o a slight absorption of alcohol around the stoppers or a slight retention of alcohol in the flask and residue. It is not possible t o recover all the alcohol from a liquid of more than 50 per cent. strength unless it is diluted with water and double the amount of distillate is collected. This multiplies the error in the specific gravity b y two and so increases the error. We have tried adding sodium chloride to the alcohol solution in the flask before distilling but i t does not seem t o affect the results. 3. Error i n Taking Specific Gravity.-An error of I point in the fourth place or say 0.9541 instead of 0.9540means a n error of about 0 . 2 per cent. alcohol and a n error of 2 points in the fourth place means a n error of 0 . 4 per cent. alcohol. The Westphal balance is not sensitive t o better than I point in the fourth place and i t requires careful work t o get it t h a t closely. The pycnometer method is more acdurate but requires a much longer time, which is a very important consideration where a large number of determinations have t o be made. 4. Temperature o j Solution when Taking Specific Gravity.-This may cause considerable error and this point must be watched very carefully. 5. Essential Oils.-Essential oils are used in most elixirs a n d in many compound fluids and tinctures. Small quantities of essential oils distil over with the alcohol and water and dissolve in the distillate. This may increase the specific gravity and lower the alcohol results. Several experiments were tried to see what effect the addition of I per cent. of essential oil would have on the assay of 50 per cent. alcohol.
Jan., 1913
It was found t h a t in a series of nine determinations the results were low from 0.9 per cent. to I .4per cent. alcohol. The effect of drug extracts on alcohol assays was also determined. A quantity of the drug extract was placed in the distilling flask with the usual amount of a n alcohol solution of known strength and the assay made in the usual way. The results were as follows: ALcoH oL Per cent Alcohol used . 49 7 Found by distillation 49 0 With extract Cascara Sagrada 48 66 With extract Gentian. . . 49 0 With extract Belladonna 48 82
..
Per cent. Per cent 51 25 56 8 50 66 56 14 50 16 56 8 49 68 55 4 50 00 55 51
From this table it will be seen t h a t while the results are about 0.65 per cent. low without the drug extracts, t h a t the average loss of alcohol is about I per cent. when the drug extracts are present. Some of the alcohol is apparently held mechanically b y the extractive matter. The writer has had occasion t o observe the results of 25 t o 30 alcohol assays per day for three or four years, and while there is little doubt that one or a dozen alcohol assays can be made which will not vary more than 0.2 per cent. or 0.3 per cent. when great care is used, still in the regular assay of a great many samples much larger errors will creep in and results may be off as much as I per cent. or 1.5 per cent. alcohol. When we stop t o consider t h a t an error of I per cent. in the alcohol assay of a single lot of 500 gallons of elixir means the addition of 5 gallons of alcohol, worth thirteen dollars, i t is really a matter of considerable importance to the manufacturer. The question now arises, how closely will pharmaceutical preparations have t o be adjusted t o the label claim t o be satisfactory under the Pure Food and Drug Law? This is a difficult question t o answer. The rule in force in this laboratory is t h a t all products must assay within I per cent. of the alcohol standard on the label before they are accepted. I t is evident, however, that there are several large pharmaceutical manufacturers who are labeling their preparations with statements of the maximum content of alcohol, but it is a n open question whether this will satisfy the requirements of the official board. The writer believes that a ruling t o the effect t h a t fluid extracts and elixirs could be labeled with the maximum content of alcohol would be just and fair and would not in any way deflect the real intent of the Drug Law. It would certainly be a welcome measure t o pharmaceutical manufacturers who are putting forth their best efforts t o conform to the law. SCIENTIFIC DEPT , PARKCE, DAVIS&. Co. DETROIT, MICH.
THE MINERALOGICAL ANALYSIS OF SOILS’ By WILLIAMH. FRY Received August 1 7 , 1912
Soil may be considered as a mixture of solid, liquid and gaseous matter. The solid matter consists of mineral and organic material which react with 1 Published
by pepmission of the Secretary of Agriculture.
]an., 1913
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
each other and with the liquid and gaseous material. By far the larger part of the solids, the d6bris of rocks, is a mixture of minerals. These minerals comprising the greater part of the soil furnish part of the socalled plant food to vegetation through the medium of the soil solution and is the chief factor influencing the texture of the soil. Much chemical work has been done upon the soil; but experience has shown that chemical analyses throw very little light upon many soil problems. So far, very little work of a purely mineralogical character has been done in connection with these problems, especially in America. This is rather surprising considering the importance of a n accurate knowledge of all soil constituents and the recent high development of petrographic methods. Work has been undertaken by the Bureau of Soils which, i t is hoped, will put the subject of soil mineralogy upon a firm basis and create interest in a silbject which cannot fail to be of great value t o both the farmer and the scientist engaged with agricultural problems. Certain generalizations concerning the component soil minerals have been established. Thus, chemical analyses have proven that the larger part of the potash and phosphatic material is concentrated in the finer mechanical separates of the soi1.I The most far-reaching and important generalization yet reached is t h a t “practically every soil contains all the common rock-f orming minerals. ’ ’ * Of course the relative proportions of soil minerals may and do vary widely. But the number of minerals that can be found in even an apparently pure quartzose beach sand is often quite large. The extreme mineralogical heterogeneity of soils is not surprising, when their origin and the various processes, both physical and chemical, t o which they are subjected are considered. All rocks, while they may consist essentially of only a few minerals, do, in reality, contain a large number of species when sufficiently large masses of the rock are considered. In the processes of weathering, the rarer mineral species are concentrated. The various weathering processes alter certain minerals, thus giving rise to other species. Wind and water, by their transporting and mixing action, add many minerals t o soils.3 Thus the mineral heterogeneity of soils is being constantly maintained. I n order to make a mineralogical analysis of a soil, certain preliminaries are often necessary and always advisable. Quartz constitutes by far the predominant part of practically all soils and i t is often convenient to eliminate this mineral from the sample in order to decrease the time which would otherwise be consumed in locating the various minerals to be determined. This elimination can be easily accomplished by means 1 G. H. Failyer. J. G. Smith and H. R. Wade, “The Mineral Composition of Soil Particles,” Bull. 64, Bureau of Soils, U. S. Department of Agriculture. ZF. K . Cameron and J. M. Bell, “Mineral Constituents of the Soil Solution,” Bull. 30, Bureau of Soils, U. S. Department of Agriculture; F. K . Cameron, “The Soil Solution” (1911); “.4n Introduction to the Study of the Soil Solution.” Jowr. P h y s . Chem., 14, 320-451 (1910). 3 E. E. Free, “The Movement of Soil Material by the Wind, with a Bibliography of Eolian Geology,” by S. C. Stunta and E. E. Free, Bw11. 68, Bureau of Soils, U. S. Department of Agriculture (1910).
3t
of heavy solutions, such as methylene iodide or Thoulet’s solution in connection with a n Harada separator or other specially constructed tubes. Minerals containing magnetic elements, as iron, can be eliminated by means of an electro-magnet. The portions from these separations will be found to lend themselves much more readily to a rapid mineralogical analysis than do the unseparated soils. I n order to separate the component minerals according to size of grain, a series of sieves supplemented by the method of centrifugal mechanical analysis’ is used. By this method the soil is separated into various portions, the diameters of the grains of each portion being constant within quite narrow limits. This separation according t o size is necessary when quantitative results are required. Various microchemical tests may be used in the determination of many of the minerals, and direct chemical tests upon the soil will often aid in the detection of the presence or absence of certain groups of minerals, such, for example, as the sulfates or chlorides. For the determination of the optical constants of the minerals, a petrographic microscope is desirable. But any microscope which can be adjusted with a condensing lens, nicol prisms, both analyzer a n d polarizer, a rotating stage, and a n eye-piece with cross hairs, can be used. After the material has been prepared for the examination, a small quantity is transferred to a microscopic slide. The material is then embedded in a n oil of a definite refractive index. A series of oils with definite refractive indices are kept for this purpose. An oil having a n index nearly equal to that of quartz serves best as a general embedding medium. The preparation is now covered with a cover glass and is ready for examination. The refractive index of any particular grain can be determined by comparison with the oil in which it is embedded. Should the indices of the mineral be either higher or lower than that of the oil, the grain will stand out with a noticeable relief. Whether the index of the grain is higher or lower can be determined by means of the Beche lines or by the method of inclined illumination of Schroeder van der Kolk.2 Various oils may be used until one is found with practically the same index of refraction as t h a t of the mineral, or the index may be roughly approximated, after a little practice, by the relief of the mineral. The index of refraction having been determined, or approximated, the other optical characteristics are determined. By crossing the nicols and rotating the stage, i t is immediately determined whether the mineral is isotropic or anisotropic, except in cases of a uniaxial mineral perpendicular to a n optic axis, in which case a n interference figure can be obtained, since isotropic minerals remain dark during the rota1 Lyman J. Briggs, F. 0. Martin and J . K. Pearce, ”The Centrifugal Method of Mechanical Soil Analysis,” Bull 24. Bureau of Soils, U . S. Department of Agriculture. 2 A detailed account of all methods used in microscopic soil mineralogy will be found in a forthcoming bulletin of this Bureau. “The Microscopic Determination of Soil-forming Minerals,” by W. J. McCaughey and W. H .
FlY.
T H E JOURNAL OF INDUSTRIAL AND ENGINEERING C H E M I S T R Y
32
tion. Should the mineral be anisotropic, whether i t is uniaxial or biaxial, is determined by means of interference figures obtained by crossing the nicols and removing the eye-piece. Uniaxial minerals give a dark cross, biaxial mineral either one or two hyperbolae according t o the optical orientation of the grain. The extinction angle can be measured by aligning a cleavage crack or crystal face of the grain with one of the cross hairs and rotating the stage until the grain becomes dark. The position or negative character of the mineral is obtained with the aid of a quartz or mica wedge or selenite plate. These characters in conjunction with the refractive index and the morphological character of the mineral, cleavage, form, and so forth, are usually sufficient t o identify the mineral. Should they not be sufficient, then further optical tests may be applied, such as the measurement of the optic angle, and so on. All of these tests can be performed very quickly. Then another mineral grain in the preparation is selected and the same procedure applied to it, until all of the grains in the preparation have been determined. Should quantitative results be. desired, they are obtained by the aid of a n eye-piece checkerwork micrometer. The minerals in the preparation being known, and all being of practically the same diameter, the percentage of any one or more species of the mineral can be gotten by count in conjunction with the micrometer as a n aid and check. So far, the limitations of the microscope have prevented the examination of the mechanical separates other than the sands and the silts. The clays, on account of the extreme minuteness of the grains, do not lend themselves t o a microscopic mineralogical analysis. A large number of analyses have been made by this laboratory and will be published in other connections where they will be fully discussed. A few only, taken more or less a t random, are given here, t o give some idea of the mineral complexity of the soil. Only one quantitative examination is included. SOILSERIES,CECIL, W. J. MCCAUGHEY (ANALYST)
. SAND 3-5 per cent. Zircon Sillimanite Rutile Microcline Plagioclase Biotite
Minerals other than quartz
SILT 10 per cent.
Abundant and characteristic mineral Sillimanite Chlorite Muscovite Orthoclase
Less abunclant or accessory minerals Garnet Hornblende Epidote Tourmaline Remarks Stretched and undulatory quartzes. Grain mostly subangular. Epidote Muscovite
From this analysis i t is seen t h a t quartz constitutes by far the larger percentage of the separates examined. I n all, fourteen minerals were determined. Some qualitative analyses of various soils are a s follows:
Jan., 19x3
Sierra Sawdy Loam frowi Sacramento Area.-Magnetite, quartz, anorthite, andesine, oligoclase, labradorite, orthoclase, microcline, hornblende, hypersthene, zoisite, muscovite, biotite, tourmaline, epidote, zircon. Orangeburg Sandy Loam.-Magnetite, quartz, oligoclase, microcline, orthoclase, albite (oligoclase-albite), labradorite, biotite, garnet, zircon, epidote, apatite (enclosed in quartz), muscovite. This soil seems very low in ferric minerals. , Norfolk Sandy Loam.-Quartz, apatite (enclosed in quartz), rutile (enclosed in quartz), tourmaline, magnetite, albite, hornblende, augite, topaz, biotite, andalusite, olivine. I t will be noticed that orthoclase does not. appear in this analysis. However, the mineral has been located in small quantities of other samples of the same soil. Sample Taken from Bed of Creek, Old Brunswick Cove.-Quartz, magnetite, andesine, labradorite, apatite, hornblende, biotite, muscovite, orthsclase. These analyses represent the sands and silts. I t is extremely probable t h a t the clays contain all of the minerals found in the separates of the larger particles. Attrition would inevitably cause particles of the larger minerals t o find their place in the clays. I n addition, it is known that the clays contain large amounts of kaolin and ferruginous matter. Chemical analyses lead us t o believe t h a t the mineralogical composition of the clays is far more complex than that of the sands and silts. Work is now in progress which it is believed will demonstrate this. The most immediate and obvious results of the mineralogical analysis of a soil is that the method gives a rapid qualitative analysis, far more rapid than the ordinary chemical methods. For instance, only a few moments are necessary t o determine whether apatite is present abundantly or otherwise. By making a quantitative examination. a n approximate idea can be formed as t o the amount in the particular soil under examination. Further, the method shows definitely in what form the chemical elements are corhbined, a result which a chemical analysis leaves t o conjecture or to probability. Something concerning t h e origin of the soil can be learned by the method. I f , for example, a soil should contain large quantities of ferro-magnesian minerals, it undoubtedly was derived largely from some basic crystalliqe rock, which particular rock would of course depend on the mineral species present taken in conjunctian with other predominant minerals of the soil. Result5 have already thrown some light on soil fertility and considerable on ground rock fertiliqer problems.1 I t is possible that the method may be the means of constructing a mineralogical classification of soils. e
BUREAUO F
SOILS
u. s. D B P A R T M ~OF~ TAGRICULTURE, WASHINGTON
1 See a forthcoming bulletin of this Bureau, “Ground Rock and Ground Minerals as Fertilizers,” by W. 0. RobinFon and W . H . Fry. “-
. 1
.-.. 1
