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.
Jute, another important fibre is readily distinguished under the microscope, for its margins have perfectly smooth walls and its lumen is wide in some places, narrow in others and interrupted altogether in places.
Photos by Flatters & Garnett
A Spider’s Foot
The toothed claws are well adapted to enable their owner to obtain a firm grasp of the fine threads of its web.
The Foot of a Fly
The two claws enable the fly to walk up rough surfaces, whilst the suckers between the claws give it a firm hold on smooth surfaces.
There are an extraordinary number of vegetable fibres which are woven into articles of commerce, of one kind and another. Then again, many fibres are so short or so brittle that they cannot be woven but are used for other purposes such as filling cushions, cheap bedding, etc. There are also a certain number of vegetable fibres which are valuable because they are stiff and bristle-like as well as durable, and they are used for brushes, door mats and for similar purposes. To the microscopist who is interested in this work there is a wide field open.
For the examination of paper, which may be described as a “felt of finely divided fibres,” the microscope is invaluable. The essentials of a good paper are that it be durable, that it retain its colour and not become brittle. The least observant of us cannot fail to have noticed that there are an extraordinary number of different kinds of paper, not only the many kinds which the paper manufacturers could show us, but the obviously varied papers which we meet with every day. Added to the papers, there are cardboards which are really a kind of paper. It is clear, therefore, that the man who can tell us exactly how any and every paper is made and what it is made of has laid up a goodly store of knowledge. In carrying out tests of paper we rely partly on chemical and partly on microscopic tests.
A number of substances contribute to the manufacture of paper; linen and cotton rags, hemp and various fibres are the most commonly used, not forgetting wood pulp which we shall mention in a moment. The finest and whitest paper is made from linen rags and that from unused linen and hemp is the strongest. Without attempting to describe in detail or even in outline the different processes which the various vegetable fibres must undergo before they appear in the guise of paper, we may say the treatment is very drastic. Strong chemicals and machinery designed to reduce the fibre to the finest possible particles render the examination of paper, for the purpose of discovering its composition, far from easy. Such fibres as survive the rough treatment are mere fragments yet they are often large enough for the lynx eyed microscope to read their story. Formerly the constituents of most papers could be separated into three classes according to their behaviour with iodine solution, but this test has been superseded by more complicated methods which do not concern us here.
The examination of various papers may prove interesting for example in linen rag paper, we ought to find some flax fibres, they will be sadly battered and torn but are usually recognisable under the microscope. Hemp paper is tough and is used for bank notes, in it some of the short tow fibres will probably occur and they will give a clue to its composition. Cotton rag paper is easily recognised for the fibres are very characteristic, a remark which also applies to jute paper, the so-called manila used for envelopes, wrappers, etc.
Mechanical wood pulp which enters so largely into the manufacture of paper is easily recognised by those who have given a fair amount of attention to the microscopical examination of plant life. Wood pulp is always used in conjunction with some binding material such as cotton or flax fibres. Many different kinds of wood are converted into pulp and of course it requires a considerable amount of experience to say exactly what kind of wood has been used in a certain paper. Some of the woods are poplars of various kinds, others spruces and firs. It is easy to distinguish the conifers as spruces and firs are called, for the reason that the trees bear cones. The little fragments of wood, scattered throughout the paper, have minute circular perforations upon them, resembling miniature quoits, if they belong to the conifers; none of the other woods possess these “pits” as they are called.
Very many other plant remains may be found in paper, for instance hop fibres are used sometimes and their presence is usually shown by remnants of the climbing hooks which, during life, studded the climbing stem of the hop.
Some of the important animal hairs, used in the manufacture of clothing, may now claim our attention. Wool and silk are of course the most important. The best wool is all obtained from the domestic sheep so let us examine one or two of the easily obtained hairs from this animal. As with the vegetable fibres we may examine them in a drop of water but, in this case, we shall find that we cannot make the water go near the wool for the reason that the latter is covered with a film of grease, called wool fat. Our first care, therefore, it to get rid of the wool fat and this may be done by shaking the specimen with a little ether or chloroform.
Having cleaned the wool fibres we may proceed to examine them under a high magnification and, to see their structure fully, we must move the fine adjustment to and fro, for it is not possible to obtain a true idea of its structure without doing so. We shall see that the hair consists of two layers, an outer skin and an inner core. The latter consists of a number of cells, whilst the former is composed of scales, of which the lower edges are arranged beneath the upper edges of the previous scales, like tiles on a roof. The free edges of the scales project outwards a little so that the wool, when not so highly magnified, appears to have a toothed margin. Further examination will show us that no single scale completely envelops the strand of wool, usually two scales make the complete circuit. It is a curious and easily tested phenomenon that in say an inch of wool from the same kind of sheep there are always the same number or very nearly the same number of scales. By counting the scales, experts can tell from what animal the wool is derived.
If we examine many samples of wool we shall not be long before we encounter certain specimens showing one or more constrictions. Now we all know that the reason why some people do not grow very much is because they are delicate, ill health affects the whole system. The constrictions in the sheep’s wool occur because the animal has suffered from some illness, or from great hunger or thirst, which has resulted in its wool not growing properly for a period corresponding to the duration of the illness or other calamity.
The examination of various animal hairs will help to while away many an hour and many of these objects are of the greatest interest. If we have the opportunity it will be interesting to compare the wool from different kinds of sheep, that from the Lincoln sheep, for example differs from that of shortwooled kinds. We may also compare goat’s wool with sheep’s, then there are differences between the hair of cows and calves. Comparisons always make microscopic work more interesting.
The microscopic examination of cloth, used for making our coats, is quite interesting work and withal important. A good deal of the cloth which is made up into suits is known as shoddy, that is to say that material that has been worn before; old rags of all sorts and many other extraordinary things go to the making of this cloth. There are special factories to which rags are sent to be made up into shoddy. One might think therefore that this substance would be easily recognised under the microscope but it is not quite so easy as we shall see. Absolutely pure wool from the sheep giving the best quality wool is only used in the very finest and most expensive fabrics. In a great deal of really good cloth we may recognise other hairs besides those of the sheep and sometimes vegetable fibres find their way into good cloth by accident. A piece of suspected cloth should be cut off and separated as far as possible into its different fibres. In shoddy we shall find few long fibres and they will all be much torn for the reason that the rags from which the material is made are cut up in the manufacture. If we find cotton fibres, we may be certain that our specimen is shoddy, also if we can find fibres of many different colours, though the final dyeing may have disguised the fact that the fibres have originally figured in fabrics of various colours.
Silk is one of the most important of all fibres capable of being woven into fabric. It is hardly necessary to remark that it is formed by the fully fed silkworm just before it turns into a chrysalis. A very large number of caterpillars spin silk but the majority of this silk is useless for commercial purposes. The silkworm gives off a double thread of silk from glands in its mouth and, at the same time, it gives off a sticky substance called silk glue which sticks the two fibres together, so that, to the eye at least they appear as one fibre.
Most of us have kept silkworms, those who have not may find it worth while to expend a few pence in some of these insects for the sake of examining the raw silk. A cocoon, as the work of the caterpillar is called, consists of three layers, an outer layer of floss, a middle layer and a so-called layer (the inner layer) of parchment. Only the middle layer is used in commerce, the floss is too fine and weak and the parchment is so impregnated with silk glue as to be useless.
If we examine some raw silk, taken from the middle layer of a cocoon, we can easily see the two parallel fibres of silk and the outer wrinkled covering of silk glue. Now, magnifying our object more highly, we shall see that each fibre is a solid rod, with a smooth lustrous surface and without any sign of lumen or cell structure; the rods too are continuous and this alone distinguishes silk from all other fibres animal or vegetable. Two tests are worth trying for they are characteristic of silk. On the addition of a little strong sulphuric acid we observe that the silk rapidly dissolves, on the other hand, if a few fibres are boiled in hydrochloric acid, the silk dissolves but the envelope of silk glue remains unchanged and appears beneath the microscope as a cracked and wrinkled tube.
The caterpillar of another moth spins coarser greyish coloured fibres, which are spun into the well known Tussore silk. As with the common silkworm these caterpillars spin two fibres and glue them together with silk glue. In this case, however, under a high magnification we shall notice that the fibres are marked with a number of very fine lines running lengthways, whilst every now and then there are fairly deep indentations. The former markings are natural to the fibres, the latter are caused by one fibre being pressed against the other. In countries where the production of silk is of great importance, the microscope is not only pressed into service for examining the product of these useful little insects, but also in keeping watch for a very deadly disease which attacks the caterpillars. It is called “pebrine” and the great scientist Pasteur, whose name is world famous for his work on bacteriology, discovered that it was caused by a tiny fungus.
Artificial silk is an important article of commerce. It is made in several different ways and of various substances. Some artificial silk is made of collodion, some again is made of cellulose the substance of which the cell walls of young plants is composed; gelatine is also used in making this commodity. As a rule it is easy to distinguish artificial from real silk, for usually the imitation consists of flat fibres or at least fibres quite different to the smooth rods of real silk. The iodine test is often sufficient indication, for with this chemical true silk is coloured brown.
Space or lack of it does not allow us to describe how the microscope may be and is applied to other manufactures, even the miller uses the instrument, for it will tell him if his flour is of pure wheat, and in this manner. He puts a little flour in a drop of water on a slide and covers with a cover slip; then, for a moment or two, he rubs the cover glass to and fro over the water and flour and examines his specimen under the microscope. If his flour be of wheat, he will see fairly stout spindle shaped strings, if it be of rye no strings appear, whilst maize flour gives very small strings. These are called gluten strings and wheat is very rich in gluten.