The Romance of the Microscope / An interesting description of its uses in all branches of science, industry, agriculture, and in the detection of crime, with a short account of its origin, history, and development

by C. A. Ealand

In how many branches of commerce, we wonder, does the microscope play its part. It is used in several departments of engineering for examining steels and many other metals not only for defects but to see how they are made up. It is used in brewing for studying the various yeasts and other substances, including the hops which go to the making of beer. All manufactures which depend upon fermentation, such as wine and vinegar making, are largely dependent upon the work of the microscope. In dairy work the microscope is invaluable. In the examination of various fabrics the assistance of the microscope is always summoned. Paper manufacture and paper testing give work for the microscopist but it would, we think, be easier to give a list of the branches of commerce in which the microscope is not used than to attempt to enumerate those which make use of the instrument.

We cannot possibly describe all the uses to which the microscope is put, so we will confine ourselves to one or two of the more important and, at the same time, to those which can, for the most part be repeated at home.

The two most important commodities for mankind are food and clothing; we cannot live without food and those of us who take but little pride in our appearance, must have clothing of some sort. We have said a little about food in another chapter and there we have also mentioned the impurities which find their way, by accident or design, into some of the commoner foods.

In this chapter we will deal first of all with clothing describing how many of the raw materials may be recognised under the microscope and showing very briefly how fraud in connection with the manufacture of wearing apparel is detected. Practically all clothing is made from animal or vegetable fibres, some, however, is made of artificial fibres and these we shall mention.

The vegetable fibres used in the manufacture of wearing apparel are all either hairs or what are called bast fibres and the latter, in non-scientific language, may be described as the strands which run through the roots and stems of most plants. The chief requirements of vegetable fibres, destined to be woven into fabrics, are strength, it is obvious that a weak fibre would be useless; length, the longer the fibre the better and as we shall see later, short fibres are often made up into inferior material; pliability, a stiff fibre would make an uncomfortable fabric; firmness and durability. Animal fibres used in the manufacture are either hairs or silk.

The most important vegetable fibre is cotton, it consists of the hairs from the seed coats of several species of Gossypium, a plant closely related to our common mallow. There are very many different kinds of cotton and the qualities of the fibres of these different cottons vary tremendously. Each hair is one cell and more or less spindle shaped, that is to say, thicker towards the middle than at the base. If we can obtain a little raw cotton we should certainly examine it under the microscope; this may best be done by laying one or two fibres in a drop of water on a slide. Under the low power, the first thing that will attract our attention is the fact that the fibres are twisted, corkscrew fashion, though not regularly nor throughout their whole length. This curious twisting makes raw cotton easily recognised and it is, at the same time, a very valuable peculiarity of these plant hairs. The greater the number of twists and the greater their regularity, the more valuable the cotton becomes for weaving purposes. Under a higher magnification, we recognise other characteristics of the cotton fibre. Each fibre is somewhat flattened, its edges are thick and, running up the centre, there is a fairly broad lumen, as it is called. Covering the whole there is a skin which by the way is often wanting in the fibres of cotton fabric owing to the chemicals with which the raw cotton has been treated and also to the methods of manufacture.

A very striking experiment may be tried by soaking a few cotton fibres in cuprammonia, a substance prepared by the action of ammonia solution on copper filings. Constrictions occur at fairly regular intervals along the fibre so that, after treatment with cuprammonia, the cotton fibres resemble strings of little beads.

The manufacture of mercerised cotton has become very important of late years. The process is named after its inventor, Mercer, and consists in removing the skin from the fibres, causing them to untwist and, by doing so, to impart to them a lustre of silk. We may make a little mercerised cotton for examination under the microscope by soaking some raw fibres for a short time in a solution of caustic soda or caustic potash and then washing them in water to which a little acid has been added. This will cause the fibres to untwist and also destroy the skin, but we shall probably notice that the fibres have shrunk. In the process of manufacture precautions are taken to prevent this shrinking for then the lustre is much better. We shall also observe that in our mercerised fibres the lumen has become very narrow and it is often broken, here and there are swellings on the outside of each fibre, corresponding to the positions of the twists. Mercerised cotton, in addition to its lustre, is stronger and absorbs dyes more easily than ordinary cotton.

Flax consists of the bast fibres of the flax plant. Examination of the raw product under the microscope will reveal both long and short fibres. The former are the more valuable and are used in the manufacture of linen, the latter are made into tow. The long fibres, which are derived from the upper parts of the flax plant have thickened edges and a very small lumen. The short fibres, used for making tow, come from the lower part of the stem and the roots of the plant. Each fibre has a broad lumen and is very similar to hemp fibre. Examination of all these fibres, by the way, is best made in water as described under cotton.

Hemp is another bast fibre and as we have remarked it resembles the short fibres of flax; there is a broad lumen with an indistinct margin. If we have an opportunity of comparing these fibres under the microscope we shall see that many of those of hemp have forked ends. This is very characteristic of the plant and is never found in flax, therefore it affords a ready means of distinguishing hemp from flax. Fine linen should never contain hemp, so that if our object be to test the quality of a sample of linen by microscopic examination, we must keep a sharp look out for the forked fibres of hemp. In coarse linen these fibres occur for hemp is used in its manufacture.