Part II Experimental Basis
The method is simple to carry out, the colors and forms that appear as fascinating and it is easy to make beautiful or sensational pictures from all kinds of mixtures and procedures. Such pictures can be enjoyed but fundamentally speaking they are mere "professorial blots" and seldomhave any scientific value. The use and effect of each stage in the process must be understood before an assesment of the results can be attempted. Every step in the procedure will be examined with the object of showing the conditions under which the best, that is the most sensitive results can be obtained.
Capillary Attraction:
Plate 25 shows four studies that were made to determine the part played by capillary attraction in this test method. For the first picture in the top row, the sap was absorbed very rapidly by laying the lower part of the paper in it as if to blot it up. Later when the sap was dry the procedure was repeated with the reagent.
For the second picture in the top row the sap rose gradually by capillary attraction. The reagent was absorbed rapidly by immersion of the paper containing the sap.
The third picture in the top row was obtained by reversing the last procedure: the sap was absorbed by immersion of the paper, the reagent rose gradually by capillary attraction.
All three pictures in the bottom row were made by setting the sap and then later the reagent to rise gradually by capillary attraction. Distinct forms, in contrast to merely colored areas appear when the reagent carrying the sap with it rises in the time set by the capillary capacity of the paper, as was the case in the last picture in the top row. The three pictures in the lower row, made with the same sap and reagent as the top pictures, show that better results are obtained when both sap and reagent rise gradually by capillary attraction.
The Order of Procedure:
The order of procedure is decided best by experiment. Two possiblities are shown in the upper section of plate 26.
The formless pictures in the top row appeared when the metalsalt was set to rise in the paper as the first stage , and the plant sap set to follow later as the second stage of the test.
In the row below, the same saps and reagent were sed for each picture as for the test immediately above it, but the order of procedure was reversed.
The form trends in fresh plant saps only appear in the test paper when the sap is set to rise first. The reagent develops the picture by rising through the sap.
The quantity of sap in relation to the paper:
The most suitable quantities of sap must be found for every type and size of paper used. As the sap must be absorbed by capillary attraction it is necessary to adjust the quantity to the capacity of the paper. This latter is determined by the texture and size of the sheet used.
Plate 26 shows two examples of the same experient with Whatman Nr.1 paper cut 14 cms wide 17 cms high. Various quantities of sap were tried, from left to right 0.5 ccm, 1.0 ccm, 1,5 ccm with double the quantity of reagent in each case.
The pictures show that 0.5 ccm spreads to widely over the paper to produce much form. Three times as much 1.5 ccm does not rise appreciabbly higher than the lesser amount. The capillaries cannot absorb so much, they tend to become blocked and the finished pictures show distorted forms. Without doubt the picturs in the middle with 1.0 ccm of sap show the most form. This quantity is most suitable for the type of paper.
In order to obtain the fullest results the quantities suitable to every type and size of paper used must be found.
The Reagent:
The top section of Plate 27 shows the experiment made to determine what quantity of reagent should be used to bring the full form content of the sap into expression. The pictures shown were made with 1 ccm of sap as this quantity was found to be the most suitable for the paper. The amount of reagent added increases from left to right, 1.0 ccm, 1.5 ccm, 2.0 ccm, 3.0 ccm. The third picture, with twice as much reagent as sap is the most fully formed. Less reagent does not bring out all the latent form, more reduces it by spreading the sap over to wide an area. For instance the clearly marked form on the right side of the third picture is only slightly shaped in the simplified picture on the right produced by too much reagent. It can be said that the optimum form in the capillary dynamic test is achieved when twice as much reagent as sap is used.
Addition of Reagent:
The l;ower section of Plate 27 shows the examples of an experiment made to decide when the reagent should be added. The pictures in the upper row were developed by adding the reagent while the plant sap was still moist or wet in the paper.
The pictures in the lower row were made in each case with the same sap as the one above, but the reagent was added some hours latter when the sap was dry in the paper.
It is clear that the sap should be dry in the paper whenthe reagent is added to complte the test.,/p> Choice of Reagent:
The filterpaper picture are all made by using a metalsalt in solution as reagent. The aim of the particular experiment usually decides the choice. The following have been tried:
Copper in the form of copper sulfate, copper nitrate, copper acetate, copper chloride. All these combinations produce green pictures with more or less fine drawing according to the state of the sap. The pictures do not alter with time.
Mercury chloride, iron sulfate, lead nitrate, uranium nitrate. Solutions of these four metalsalts develop very pale pictures with the same kind of fine brown drawings as described in the pictures developed with solutions of copper salts. They do not change with time.
Gold in the form of gold chloride develops pictures with abundant form and great variety of color. The latter become slightly deeper in tone as the pictures age.
Silver nitrate although colorless when rising in the paper soon darkens. Many shades can appear: rust, gray brown, even green vary the generally rich brown tones of the main test area. The pictures may keep for years or under the same conditions loose their color completely. This quality of silver, so valuable in assesing the test, has led many users to discard it as a reagent for examining plant saps.
For general use gold chloride and silver nitrate used separately to develop pictures of the same sap give the most comprehensive results, silver for the fine details of form, gold for the variable color combinations that appear.
it should be added that only metalsalt combinations that are soluble in water are to be used. Solutions in alcohol evaporate too quickly when rising in the paper..
The Use of More than one Reagent on the same Test:
Metalsalt in solution react on each other, and the reaction becomes visible in the paper according to the time of mixing (bibl. 3,38). The plant can asset itself against the metalsalt solutions, but its formative power will appear less clearly than when only one reagent is used to draw it out.
Gold chloride and silver nitrate used tohgeather as reagents on the same sap "fix" each other. The pictures can be exposed to light without harmful effects, but they are poor in quality. They lack the subtle colors of the gold pictures and show very little of the detailed formation of the silver ones.
Silver nitrate is someties set to rise through a test already developed by some other reagent. The silver solution covers some forms paritally, others completly and so confuses the result. The pictures may look impressive but they lose their full value by this procedure. Similarly nothing is gained by setting water to rise as a second reagent through the finished test. Itis better to use a weaker concentration of sap or reagent from the start.
Summary on Method Analysis:
Certain rules must be kept in order to achieve the fullest and most sensitive results.
- Sap and reagent must rise by capillary attraction.
- The sap should be set to rise first and then the reagent
- The sap should be dry in the paper when the reagent is added
- The quantities best suited to the size and type of paper should be found.
- Twice as much reagent as sap develops the picture fully.
- Only one reagent should be used for each paper. The reaction of the plant sap to various metalsalts is best examioned by means of a series of parallel test. For general use gold chloride and silver nitrate give the most all round results
Variations In Technique
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