General Science by Bertha May Clark (best historical fiction books of all time TXT) π
[Illustration: FIG. 9.--Determining one of the fixed points of a thermometer.]
The Centigrade thermometer, in use in foreign countries and in all scientific work, is similar to the Fahrenheit except that the fixed points are marked 100Β° and 0Β°, and the interval between the points is divided into 100 equal parts instead of into 180.
The boiling point of
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227. The Selection of Dyes. When silk and wool, cotton and linen, are tested in various dye solutions, it is found that the former have, in general, a great affinity for coloring matter and acquire a permanent color, but that cotton and linen, on the other hand, have little affinity for dyestuffs. The color acquired by vegetable fibers is, therefore, usually faint.
There are, of course, many exceptions to the general statement that animal fibers dye readily and vegetable fibers poorly, because certain dyes fail utterly with woolen and silk material and yet are fairly satisfactory when applied to cotton and linen fabrics. Then, too, a dye which will color silk may not have any effect on wool in spite of the fact that wool, like silk, is an animal fiber; and certain dyestuffs to which cotton responds most beautifully are absolutely without effect on linen.
The nature of the material to be dyed determines the coloring matter to be used; in dyeing establishments a careful examination is made of all textiles received for dyeing, and the particular dyestuffs are then applied which long experience has shown to be best suited to the material in question. Where "mixed goods," such as silk and wool, or cotton and wool, are concerned, the problem is a difficult one, and the countless varieties of gorgeously colored mixed materials give evidence of high perfection in the art of dyeing and weaving.
Housewives who wish to do successful home dyeing should therefore not purchase dyes indiscriminately, but should select the kind best suited to the material, because the coloring principle which will remake a silk waist may utterly ruin a woolen skirt or a linen suit. Powders designed for special purposes may be purchased from druggists.
228. Indirect Dyeing. We have seen that it is practically impossible to color cotton and linen in a simple manner with any degree of permanency, because of the lack of chemical action between vegetable fibers and coloring matter. But the varied uses to which dyed articles are put make fastness of color absolutely necessary. A shirt, for example, must not be discolored by perspiration, nor a waist faded by washing, nor a carpet dulled by sweeping with a dampened broom. In order to insure permanency of dyes, an indirect method was originated which consisted of adding to the fibers a chemical capable of acting upon the dye and forming with it a colored compound insoluble in water, and hence "safe." For example, cotton material dyed directly in logwood solution has almost no value, but if it is soaked in a solution of oxalic acid and alum until it becomes saturated with the chemicals, and is then transferred to a logwood bath, the color acquired is fast and beautiful.
This method of indirect dyeing is known as the mordanting process; it consists of saturating the fabric to be dyed with chemicals which will unite with the coloring matter to form compounds unaffected by water. The chemicals are called mordants.
229. How Variety of Color is Secured. The color which is fixed on the fabric as a result of chemical action between mordant and dye is frequently very different from that of the dye itself. Logwood dye when used alone produces a reddish brown color of no value either for beauty or permanence; but if the fabric to be dyed is first mordanted with a solution of alum and oxalic acid and is then immersed in a logwood bath, it acquires a beautiful blue color.
Moreover, since the color acquired depends upon the mordant as well as upon the dye, it is often possible to obtain a wide range of colors by varying the mordant used, the dye remaining the same. For example, with alum and oxalic acid as a mordant and logwood as a dye, blue is obtained; but with a mordant of ferric sulphate and a dye of logwood, blacks and grays result. Fabrics immersed directly in alizarin acquire a reddish yellow tint; when, however, they are mordanted with certain aluminium compounds they acquire a brilliant Turkey red, when mordanted with chromium compounds, a maroon, and when mordanted with iron compounds, the various shades of purple, lilac, and violet result.
230. Color Designs in Cloth. It is thought that the earliest attempts at making "fancy materials" consisted in painting designs on a fabric by means of a brush. In more recent times the design was cut in relief on hard wood, the relief being then daubed with coloring matter and applied by hand to successive portions of the cloth. The most modern method of design-making is that of machine or roller printing. In this, the relief blocks are replaced by engraved copper rolls which rotate continuously and in the course of their rotation automatically receive coloring matter on the engraved portion. The cloth is to be printed is then drawn uniformly over the rotating roll, receiving color from the engraved design; in this way, the color pattern is automatically printed on the cloth with perfect regularity. In cases where the fabrics do not unite directly with the coloring matter, the design is supplied with a mordant and the impression made on the fabric is that of the mordant; when the fabric is later transferred to a dye bath, the mordanted portions, represented by the design, unite with the coloring matter and thus form the desired color patterns.
Unless the printing is well done, the coloring matter does not thoroughly penetrate the material, and only a faint blurred design appears on the back of the cloth; the gaudy designs of cheap calicoes and ginghams often do not show at all on the under side. Such carelessly made prints are not fast to washing or light, and soon fade. But in the better grades of material the printing is well done, and the color designs are fairly fast, and a little care in the laundry suffices to eliminate any danger of fading.
Color designs of the greatest durability are produced by the weaving together of colored yarns. When yarn is dyed, the coloring matter penetrates to every part of the fiber, and hence the patterns formed by the weaving together of well-dyed yarns are very fast to light and water.
If the color designs to be woven in the cloth are intricate, complex machinery is necessary and skillful handwork; hence, patterns formed by the weaving of colored yarns are expensive and less common than printed fabrics.
CHAPTER XXIV CHEMICALS AS DISINFECTANTS AND PRESERVATIVES231. The prevention of disease epidemics is one of the most striking achievements of modern science. Food, clothing, furniture, and other objects contaminated in any way by disease germs may be disinfected by chemicals or by heat, and widespread infection from persons suffering with a contagious disease may be prevented.
When disease germs are within the body, the problem is far from simple, because chemicals which would effectively destroy the germs would be fatal to life itself. But when germs are outside the body, as in water or milk, or on clothing, dishes, or furniture, they can be easily killed. One of the best methods of destroying germs is to subject them to intense heat. Contaminated water is made safe by boiling for a few minutes, because the strong heat destroys the disease-producing germs. Scalded or Pasteurized milk saves the lives of scores of babies, because the germs of summer complaint which lurk in poor milk are killed and rendered harmless in the process of scalding. Dishes used by consumptives, and persons suffering from contagious diseases, can be made harmless by thorough washing in thick suds of almost boiling water.
The bedding and clothing of persons suffering with diphtheria, tuberculosis, and other germ diseases should always be boiled and hung to dry in the bright sunlight. Heat and sunshine are two of the best disinfectants.
232. Chemicals. Objects, such as furniture, which cannot be boiled, are disinfected by the use of any one of several chemicals, such as sulphur, carbolic acid, chloride of lime, corrosive sublimate, etc.
One of the simplest methods of disinfecting consists in burning sulphur in a room whose doors, windows, and keyholes have been closed, so that the burning fumes cannot escape, but remain in the room long enough to destroy disease germs. This is probably the most common means of fumigation.
For general purposes, carbolic acid is one of the very best disinfectants, but must be used with caution, as it is a deadly poison except when very dilute.
Chloride of lime when exposed to the air and moisture slowly gives off chlorine, and can be used as a disinfectant because the gas thus set free attacks germs and destroys them. For this reason chloride of lime is an excellent disinfectant of drainpipes. Certain bowel troubles, such as diarrhΕa, are due to microbes, and if the waste matter of a person suffering from this or similar diseases is allowed passage through the drainage system, much damage may be done. But a small amount of chloride of lime in the closet bowl will insure disinfection.
233. Personal Disinfection. The hands may gather germs from any substances or objects with which they come in contact; hence the hands should be washed with soap and water, and especially before eating. Physicians who perform operations wash not only their hands, but their instruments, sterilizing the latter by placing them in boiling water for several minutes.
Cuts and wounds allow easy access to the body; a small cut has been known to cause death because of the bacteria which found their way into the open wound and produced disease. In order to destroy any germs which may have entered into the cut from the instrument, it is well to wash out the wound with some mild disinfectant, such as very dilute carbolic acid or hydrogen peroxide, and then to bind the wound with a clean cloth, to prevent later entrance of germs.
234. Chemicals as Food Preservatives. The spoiling of meats and soups, and the souring of milk and preserves, are due to germs which, like those producing disease, can be destroyed by heat and by chemicals.
Milk heated to the boiling point does not sour readily, and successful canning consists in cooking fruits and vegetables until all the germs are killed, and then sealing the cans so that germs from outside cannot find entrance and undo the work of the canner.
Some dealers and manufacturers have learned that certain chemicals will act as food preservatives, and hence they have replaced the safe method of careful canning by the quicker and simpler plan of adding chemicals to food. Catchup, sauces, and jellies are now frequently preserved in this way. But the chemicals which destroy bacteria frequently injure the consumer as well. And so much harm has been done by food preservatives that the pure food laws require that cans and bottles contain a labeled statement of the kind and quantity of chemicals used.
Even milk is not exempt, but is doctored to prevent souring, the preservative most generally used by milk dealers being formaldehyde. The vast quantity of milk consumed by young and old, sick and well, makes the use of formaldehyde a serious menace to health, because no constitution can endure the injury done by the constant use of preservatives.
The most popular and widely used preservatives of meats are borax and boric acid. These chemicals not only arrest decay, but partially restore to old and bad meat the appearance of freshness; in this way unscrupulous dealers are able to sell to the public in one form or other meats which may have undergone partial decomposition; sausage frequently contains partially decomposed meat, restored as it were by chemicals.
In jams and catchups
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