A line of unknown dimensions, equal to 5-6 divisions of the eye-piece scale, when examined with the 4-inch objective, eye-piece C, and the tube racked out to its full length of 10 inches, would be (022 by 5-6) millimetres, that is, 0.1232 millimetre long.

The apparatus described is obviously very simple in character, and easy to manipulate. A little practice on fibres of known length will soon give the student confidence in his ability to measure other fibres or to determine the extent to which the fibres have been shortened by the process of beating.

This latter determination is a matter of considerable difficulty, however, which requires the measurement of a large number of fairly typical fibres in order to arrive at an approximately accurate average figure. With short fibres, such as straw and grass, the measurement is comparatively easy, but in the case of long fibres, like cotton, linen and hemp, a good deal of judgment is necessary, on account of the great differences in the length of the individual beaten fibres. Comparative readings under suitable conditions will give useful information when carefully taken. Cotton pulp is easier to deal with than hemp, for example, since the beaten fibres are more definite in shape and less liable to produce masses of fibrille, which tend to render measurement difficult.

With unbeaten pulp in which the fibres, as a whole, are present in the maximum length, the differences may not be great in the sample under examination, though for certain vegetable species the age of the plant will, to some extent, determine the average length of the ultimate fibre.

Reagents for Microscope Work.

The work of identification of fibres would certainly be much simplified if it were possible to find definite colour reagents, capable of giving colours on the surface of the sheet of paper as in the case of the presence of mechanical wood pulp in a paper, where the use of some special reagent like aniline sulphate, or phloroglucine, is resorted to.

When reagents have been discovered for paper-testing which are as definite in their colour reactions for other fibres, then the work of differentiation will be much simpler. At present the microscope is the only safe means of identification and even then it is frequently impossible completely to analyse the mixture of fibres in a well-beaten paper.

For ordinary purposes the identification of fibres is assisted by means of a solution of iodine.

This reagent usually gives the following results :

(1) Fibres coloured yellow.

1. Mechanical wood.

2. Jute.

(2) Fibres not coloured.

1. Wood cellulose.

2. Straw cellulose.
3. Esparto cellulose.

(3) Fibres coloured brown.

1. Cotton.

2. Linen.

3. Hemp.

Now the effect of any special solution by which the fibres are coloured, is not merely one of coloration. The reagent serves to intensify the differences of structure, and brings out the structural details more clearly.

It is important in microscope work to employ a solution of known strength. Unless this is done variations in the intersity of colour will be observed and these variations are apt to lead to confusion in results.

In using reagents for the examination of fibres under the microscope variations in the colour effects are liable to occur under the following conditions:

(1) The use of reagents of unknown strength. It is advisable always to work with a solution of standard composition, so that results may be readily compared.

(2) The condition of the pulp will, of course, modify the intensity of colour; if the small quantity of fibre put on the glass slip is very moist it will not take so dense a colour as a similar portion squeezed out fairly dry by means of blotting paper.

(3) The physical condition of the fibres under investigation is an important factor in the colour reaction. The appearance, for example, of cotton fibre will vary according to the treatment it has sustained.

This can be seen by examination of a piece of cotton, first raw, then in a piece of old cotton rag, and again in the same rags after boiling, and, finally, after being thoroughly beaten and ready for making into paper.

(4) The purity of the cellulose itself has also a marked influence upon the colour reactions. The truth of this statement can easily be verified by examination of specimens of imperfectly boiled wood pulp, and samples prepared from over-boiled wood. The structural details are much more marked in the former

case.

(5) The length of time during which the fibres are exposed to the influence of the reagent also causes variation in colour. Iodine, especially, is a fugitive reagent, and fibres showing a dense colour at first will gradually lose the colour and eventually appear almost colourless.

The list of solutions in use is as follows:

Taking the case of iodine we find the following formulæ in use by various well-known experts:

The second reagent and one which is exceedingly useful is the zinc chloride and iodine solution.

This reagent gives a clear distinct result in many cases, but it is impossible to state that this solution is always to be preferred to iodine. Much depends upon the condition of the beaten pulp.

The following solutions are those usually employed :

These reagents are well known to those accustomed to employ the microscope for the identification of fibres, but there are certain reagents perhaps less well known, which are exceedingly valuable under special circumstances.

Dr. Winkler suggests the employment of magnesium chloride in the place of zinc chloride, using the substance in combination with iodine, according to the following formula:

Magnesium chloride (saturated solution).
Iodine solution (Winkler's formula)

50 c.c.

2.5 ??

Another useful reaction for identifying fibres, or for intensifying the appearance of the structural details is that in which sulphuric acid acts upon the fibres after they have been stained with the usual iodine solution.

The formulæ for the solutions are as follows:

(A) Potassium iodide.

1 gramme. 100 c.c.

Iodine, to saturate (add 2 crystals of iodine to solution).

(B) Concentrated glycerine.

Water.

Add sulphuric acid (1-78 sp. gr.) slowly

20 c.c.

10 "" 30

The fibre is mounted in iodine solution as usual, and covered.

A drop of acid is placed on the slide in close contact with the cover-glass and drawn in by the capillary attraction of a piece of blotting paper held on the slide near the coverglass on the side opposite the acid. This is explained by Fig. 136.

C

a

b

Fig. 136. -- Diagram to illustrate Method of staining Fibres by “Irrigation."
a. Piece of blotting paper.
b. The glass slip.

c. The cover-glass.
d. Drop of sulphuric acid.

The blotting paper soaks up the liquid under the cover-glass and thereby draws

in the drop of sulphuric acid under the cover-glass, and the fibres are stained,

A useful reaction, particularly for lignified fibres and for pulp which has been partially prepared, is that produced by the use of chlorine water and a solution of sodium sulphite.

The solutions for this test are prepared as follows:

Chlorine water.

Pass chlorine gas into water until the latter is saturated.

The chlorine water acts upon the fibres, producing a slight yellow coloration, and the addition of sodium sulphite to the chlorinated fibre produces a more or less deep magenta colour, which serves to bring out the structural detail more clearly.

Another distinctive test for lignified tissue, particularly wood pulps, is the ferric-ferricyanide reaction, which produces a marked blue coloration in the fibre, due to the formation of prussian blue in the cells of the fibres.

The formulæ as suggested for the reaction by Cross and Bevan are:

Mix equal volumes of these two solutions when required.

The well-known phloroglucine reagent is prepared as follows:

Phloroglucine
Alcohol
Hydrochloric acid

4 grammes. 100 c.c.

50 ""

The differentiation of various fibres by the use of aniline dyes has been fully studied by Professor Behrens.

The more frequently used dyes are magenta, methylene blue, eosin, diphenylamine blue, these solutions being most conveniently prepared with a strength of 1 in 2000.

These dyes act differently with various fibres, and Behrens claims that it is possible to make use of them as a means of identification, when applied under precise and definite conditions. He states that it is possible to obtain very marked differences with similar fibres by means of "combination "results. That is to say, fibres treated with one aniline colour, will subsequently yield marked differences in colour when further treated with a second dye. In the identification of hemp and flax, which usually proves to be a difficult operation, Behrens obtains what he terms a "combination" colour by treating the mixture of fibres with malachite green and then subsequently with benzopurpurin.

The effect of this double combination is that the hemp appears green and the flax appears a brick-red colour.

There is plenty of scope for further investigation into this question of the identification of fibres. Thus, for instance, the close resemblance of cotton and linen fibres in a well-beaten paper makes the task of determining the proportions of cotton and linen an exceedingly difficult one, and it is very much to be questioned whether an analysis made with the microscope can give in precise

terms and figures the correct proportions of cotton and linen in a paper said to be made from rags.

In a case of this kind much experience is necessary in order to arrive at a satisfactory conclusion, although at the same time it is well to bear in mind that an estimate which comes within 10 per cent. is often sufficient for practical purposes.

The only instances in which the identification is of absolute importance is that in which the presence or absence of cotton in a linen paper, or of linen in a cotton paper, for example, might be considered a sufficient excuse for rejecting a delivery of paper, but this is in itself an extremely unlikely case.

TABLE XXVII.-Micro-chemical Reactions of Fibres.