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apparent at the bottom of the tube. When cool the entire mixture was colored a light slate color, from a glight precipitate of silver.
By direct experiment I find that chemically pure stearin may be boiled in a solution of the nitrate of silver without suffering discoloration, and from the fact that no deposit of metallic silver appears in the silver solution employed it is evident that stearin under this condition does not deoxidize nitrate of silver.
Palmitin, marked chemically pure, treated in the same manner, exhibits properties very much like those of stearin. This fat when cooled presents a pure white color, but I have observed that the silver solution was slightly darkened on boiling. I think probably the sample of palmitin used contained a trace of olein,
Commercial oleo, beef oil, an extract of beef fat, is composed largely of the olein or oil of beef fat. It also contains palmitin, and a very small percentage of stearin. Boiled with the nitrate of silver solution, the solid fat of the oil retains its original color, but the oil proper causes a slight darkening of the solution.
By these experiments it will appear that neither stearin nor palmitin deoxidizes silver. Should this prove correct, it will appear evident that the pure oil of beef fat decomposes the silver to a very limited extent. If soft commercial stearin, which contains a trace of beef oil proper, is tested in the same way, it will be observed that while the stearin is not affected the beef oil causes a slight precipitation of silver, as in the case of commercial oleo.
Pure and perfectly fresh leaf lard treated as above is not changed in color, neither does it precipitate silver from the diluted solution, but late experiments demonstrate that if pure lard is exposed to the atmosphere of a warm room for several days its chemical properties are somewhat changed, and on testing it with the silver solution not only is the silver solution darkened but the hot lard becomes brown and a dark precipitate of silver is formed.
A sample of the same lard exposed for three days longer, on being tested in the same manner, showed conclusively, on being heated to the boiling point of the silver solution, an increase of brown coloration of the liquid, together with a dark precipitate of silver in the silver solution at the bottom of the tubé. On standing for thirty minutes a dark ring of silver precipitate is observed resting on the surface of the silver solution. In connection with these experiments I tested in the same way a sample of pure leaf lard which I had rendered myself in June last. This lard had been continuously exposed to light and air in a temperature of about 75°F. On treating this sample of the lard with the silver solution, silver began to fall quickly in the solution as the temperature increased, until its density had become such that a solid gray mass of silver apparently filled the bottom of the test tube to the depth of half an inch, and the liquid lard had become quite brown in color.
The lard when cold (congealed) has a slight brownish tinge, but on remelting it, it appears quite brown and translucent by reflected light; by transmitted light it appears light brown and translucent.
It will be seen by these experiments with lard and the silver test, that the condition of the lard as regards freshness must be considered, otherwise pure lard that is slightly acid from exposure may be condemned as adulterated, or as being a compound of lard and cottonseed oil.
In England at the present time, under the silver test, a person may be sent to the penitentiary for selling pure lard, because of the honest
conviction of some experts that lard exhibits no reaction with the silver solution.
SILVER TEST FOR OLIVE OIL.
In the following experiments the olive oil and other oils treated are from sources which I know to be reliable. Samples of our native olive oil were furnished me by Mr. S. S. Goodrich, proprietor of the Quito Olive and Vine Farm, California, and by the Messrs. Wright Brothers, Riverside, California. The seed oils were obtained from the late F. S. Pease, manufacturer of fats and oils, Buffalo, New York.
I found early in my investigation that owing to a difference in the physical properties of the oils, all the spectrum colors might be produced by regulating the strength of the silver solution, subjecting the mixtures to a uniform heat; the color-reactions of certain oils will be observed more quickly than others. Most of the oils when boiled with a saturated solution of the nitrate of silver for one minute will precipitate a portion of silver, some more some less in amount, and in some cases the bright silver is deposited on the wall of the tube opposing the column of oil. But pure olive oil treated with a saturated solution of the nitrate of silver is not as satisfactory in behavior as when a diluted solution is used. I have found that by diluting the saturated solution 50 per cent with distilled water I obtained better results, but that by a still weaker solution the results are still more satisfactory; greater divergence of color and stronger tints are obtained in all the oils.
The solution I have used in these experiments consists of an ounce of the concentrated solution to 2 ounces of distilled water well mixed in a stoppered bottle. With this solution I proceed as follows: Test-tubes five eighths of an inch in diameter and 6 inches in length are arranged in a suitable rack, and numbered from 1 to 7, respectively. No. 1, pure olive oil; No. 2, pure lard oil; No. 3, cotton-seed oil; 4, poppy-seed oil; 5, peanut oil; 6, oil of sesame (benne oil); 7, colza oil. A well-fitting cork is provided for each tube, and a spirit lamp placed conveniently. Into each tube I pour 2 cubic centimeters of the silver solution, following it with 4 cubic centimeters of the oil in the order given above. Each tube is tightly stoppered to prevent staining the fingers and is well shaken, so that the solution will be intimately mixed with the oil. The corks are then removed and the tubes replaced in the rack. At this stage it will be observed that the oils appear to have changed color, becoming more or less cloudy and of different tints or shades of color. This change of color and cloudiness arises from the precipitation of natural fats of the oils, which finally fall and rest on the surface of the silver solution. I then boil each mixture, holding the tube over the flame of the lamp, moving it backwards and forwards until the clear silver solution boils. With an adequate flame the time required for this process should not exceed one minute for each sample. Observe changes of color as they occur.
No. 1. Pure olive oil. Natural color a greenish yellow, with a nutty flavor. The clear silver solution on boiling for one minute exhibits a whitish bloom owing to a slight reduction of silver, but soon clears. If properly heated the oil will change to a well-defined light sienna color, translucent owing to the precipitate of fat, but with no deposit of silver. At this stage of the experiment sometimes, from overheating, a shade of silver may be observed on the tube wall opposing the oil column near the surface of the silver solution. In this case the oil is much darker. This observation is important from what follows on heating the other oils.
No. 2. Pure lard oil. Natural color light straw. The silver solution is slightly darkened on boiling, and a slight deposit of silver falls to the bottom of the test tube. In the course of several days the oil appears lighter in color and translucent, owing to the deposit of fat.
No. 3. Cotton-seed oil (unbleached). Natural color deep yellow. The silver solution is slightly darkened, afterwards clearing. The color of the oil changes to a reddish yellow, and the tube wall on cooling is generally spotted with silver. Rancid lard oil yields more of the silver precipitate than the fresh oil.
No. 4. Poppy-seed oil. Natural color deep yellow. The silver solution becomes reddish brown changing to black. This, later, coagulates and becomes jet-black, rising to the surface of the silver solution. This feature is constant. The oil above is cloudy from the precipitate of natural fat, and changed in color to a greenish yellow, but after standing several days the dark fat precipitates and the oil becomes clear. 'A very slight deposit of silver is observed at the bottom of the tube, after twenty-four hours.
No. 5. Peanut oil. Natural color light straw. The silver solution is slightly darkened, with a light deposit of silver at the bottom of the tube. Bright specks of silver appear on the tube walls opposing the silver solution. A light orangecolored congealed fat soon deposits on the surface of the silver solution. The oil becomes perfectly clear and of a pale sienna color. After several days the precipitated fat changes in color from orange to bright chrome yellow and a very heavy bright deposit of silver falls to the bottom of the test tube.
No. 6. Oil of sesame (benne). Natural color very light greenish yellow. The silver solution is slightly darkened. Later it clears up colorless. Slight deposit of silver. The oil changes to a light straw-color on precipitation of its fat, which rests on the silver solution.*
No. 7. Colza oil. Natural color light greenish yellow. Heated with the silver solution, colza oil becomes saffron color viewed by transmitted or reflected light; after several days changes to a very dark amber viewed by transmitted light. The silver solution exhibits a slightly yeliow color on heating, but clears depositing silver lightly at the bottom of the test-tube. On standing for thirty-six hours silver specks are seen on the tube wall opposing the oil column.
Having acquired a knowledge of the properties of the individual oils, as above, I proceed to combine them respectively and individually with the pure olive oil and silver solution and note results, using the same proportions of each mixed oil with 2 cubic centimeters of the silver solution as in the experiments with the individual oils, observing the same method of treatment:
No. 1. Pure olive oil and pure lard oil, 4 cubic centimeters of each, to which is added 2 cubic centimeters of the silver solution.
No silver is thrown down in the silver solution during the heating process, but after standing several days a very light silver precipitate is frequently observed on the tube wall opposing the oil. Color a light straw, lighter than that of either oil when treated singly.
No. 2. Olive and cotton-seed oil. On boiling olive and cotton-seed oil a very slight dark shade sometimes occurs in the silver solution which clears on cooling. No silver is thrown down to the bottom of the test-tube if the cotton-seed oil is perfectly fresh. On standing several days a narrow band of orange-colored fat appears rest
* Olive and sesame oils may be tested to profit by either the nitric or the sulphuric acid tests given in my last annual report to the Secretary of Agriculture, volume page
197. • Test A, 55 parts sulphuric acid chemically pure, combined with 45 parts distilled water, by measure. Specific gravity 1.575, temperature 71.6° F., 220 C.
“ Test B, 55 parts sulphuric acid chemically pure, combined with 30 parts distilled water, by measure. Specific gravity 1.648, temperature 71.1° F., 220 C.”
If the oil of sesame is present in olive oil, it may be detected by either test A or B. By the former as small an amount as 5 per cent will be indicated. By test B a well-defined violet tinge is seen in the lower layer of the tube, and above this, about midway of the tube, a dark band characteristic of the oil of sesame is observed. The color reactions of the oil of sesame treated with test A are different from the color reactions with test B (see Plate 4, Figs. 3, 4). See also in same report nitric acid test for olive oil, which distinguishes it from all other oils, lard oil excepted.
ing on the silver solution. The oil appears a clear light straw-color by transmitted light, dark brown color by reflected light after the lapse of several days. The tube wall is spotted with the silver deposit.
No. 3. Olive and poppy-seed oil. Light deposit of silver at the bottom of the tube. Light brown deposit of natural fat with particles of the fat light brown in color dusting the wall of the tube. No deposit of silver is observed after standing for several days. Color of the oil, light yellow by reflected light and the same by transmitted light.
No. 4. Olive and peanut oil. A heavier deposit of silver appears in the silver solution, but none is seen in the oil column. The oil appears translucent from precipitation of natural fat and becomes an orange color. After eight days the color changed to a chrome yellow.
No. 5. Olive and sesame oil. A light deposit of silver on the tube wall opposing the oil column, the silver solution is clear. The color of the oil by reflected light is a dark amber, viewed by transmitted light it appears a lighter shade of same color. There is a heavy deposit of natural fat brick-dust-red in color, the low ar stratum of which appears a light brown.
No. 6. Olive and colza oil. This mixture when combined before heating appears translucent and a very light straw-color, clearing at the surface of the oil quickly, the fats falling to the bottom of the oil column. On boiling, the oil becomes a deep shade of ochre. No bright silver precipitate is observed at this stage.
In the absence of colored illustrations it is difficult to convey an accurate knowledge of the color-changes herein described. I therefore recommend strongly that duplicates of all experiments be made, as strict uniformity of color can not always be attained, and in duplicating one will soon perceive, owing to slight difference in results, that a sample may have been overheated while another has been underheated.
In a series of experiments made with a variety of oils using the saturated solution of nitrate of silver precipitates of silver were obtained in each case. After several weeks' exposure to light, the amount of allotropic silver was found to be much increased. (See plates 7, 8, 9, and 10.)
MUSHROOMS OF THE UNITED STATES.
Since the publication of my first report on the edible mushrooms of the United States, which appeared originally in the annual volume of this Department for the year 1875, there has been a continuous demand for information on this subject, applications for copies of that paper having been received from nearly every State of the Union. My present report contains descriptions and illustrations of eight additional species of edible mushrooms common to the United States, together with simple and improved methods of mushroom culture and some recipes for preparing mushrooms for the table which may be welcome in localities where as yet this savory, nutritious, and abundant comestible has not been utilized. Twelve of the poisonous varieties are also described and their distinguishing characteristics illustrated.
Before selecting mushrooms from field or forest inexperienced persons would do well to consider first carefully the descriptions of the characteristics of edible and poisonous varieties given in the respective plates. The taste and odor of a mushroom is quite significant and it would be well to reject all mushrooms found growing in filthy places. The colors of mushrooms should also be carefully observed. A redtopped mushroom with yellow or tan-colored gills, white or pink stalk, is edible, while a red-topped mushroom with white gills and a white stem, is poisonous. The common puff-ball for table use