Sewage.— It has been found that sewage, if aerated or "activated' as it is called, by letting air bubble through tanks containing it, will separate by oxidation into two types of bodies; the sludge, which precipitates and is available as a nitrogen fertilizer, and the efflu ent, which is a clear solution. By treating the effluent with chlorine. its danger as a carrier of disease is removea and it ceases to pollute the streams into which it flows. The economic treatment of city sewage, so that the recovery and sale of inoffensive sludge as fertilizer pays the cost while the pollution of rivers and har bors is brought to an end, has not yet been generally attained. Of considerable promise is the Miles process whereby sulphur dioxide is mixed with the sewage which reduces all the soaps and fats. With the fats removed by means of a recoverable organic solvent, the sludge is good nitrogen fertilizer. The outlook for its early achievement is favorable.
Paper.— There are certain combinations of carbon and hydrogen that are known as sugars. There are many of them, but they are all alike in that they are made tip of carbon atoms strung together as in a chain, with hydrogen and oxygen atoms stuck on along the side of the chain. Now suppose you take a number of these sugar molecules, as the smallest particles Imaginable are called, and bunch them together, so that a lot of these units are combined into one big complex one. Then you have a series of resins or gums and starch. This is what chemists call polymerization. Now let us take these resins and by chemical chicanery and tricks cause them to bunch their molecules again, to- polymerize, and, if we carry it far enough, we get cellulose. That is, we should if we could. But trees and plants do this with ease; they start with water and carbonic acid gas, from the air, and this they manufacture into sugar, the sugar into starches, gums and other things, and finally into cellulose, of which their cells are made. Cellulose is the frame work of cells, and all organic life is made up of it, with juices and sap and solutions of one sort or another wandering around within them. Cotton is nearly pure cellulose. Paper is cellu lose; little filaments of it, matted or felted to gether.
Now the varieties of cellulose and the dif ferences in their structure, both physical and chemical, are beyond the knowledge of to-day. Cotton, as we have already said, is nearly pure cellulose and yet there are 60 different varie ties of it listed, and they all differ from each other in the structure of their fibres. So we may say that the art of making paper, which has already entered the list of chemical manu facture, is one that presents innumerable un solved problems.
The main source of available supply is wood. Mechanical pulp, which is the cheapest, con sists in the fibres of soft wood, torn asunder by grinding diagonally the edges of the natural wood with a stone, in the presence of water. Their particles contain a large part of the gums and other substances of the tree which are less stable than cellulose. So they oxidize on long exposure and the process of oxidation, whether it be slow as in this instance or rapid as with fire, is likely to be contagious, and the cellulose is in time changed to oxy-cellulose, which is an amorphous powder with no mechan ical qualities whatever. That is why news
paper lacks durability. It also explains why old-fashioned hand-made paper, made of linen rags, is more durable than modern paper, even though it be made of linen, too. The chemical treatment is more severe and drastic in the modern machines than in the old hand beaters, whereby the chemical structure of the cellulose seems to be attacked and thus rendered more susceptible to oxidation.
A better quality of pulp is made by the sul phite process, discovered by a Philadelphia chemist named Tilghman. It consists in treat ing chips of wood with a solution of calcium bisulphate, with a view to dissolving out by the sulphurous acid which is set free all organic substances except the cellulose. It takes place under heat and pressure. The cellulose fibres of the chips are then bleached and treated with water and strained until they are thoroughly separated from each other. It requires about 20 per cent of sulphite pulp mixed with the mechanical product to make a good quality of newspaper.
A stronger quality of sulphite pulp is pro vided by the Mitscherlich process in which a weaker acid is used. This points the way to improvements in the art such as the lately de veloped, so-called Kraft paper, a very strong wrapping paper made of undercooked sulphite pulp. This has developed into what is known as the °sulphate process,' which, by its milder chemical treatment of the wood, is finding in creased application.
The tendency of research in the preparation of pulp is to conserve the chemical structure of the cellulose and to find new sources of sup ply, owing to the using up of spruce and other soft-wood forests for this purpose. The United States consumes from four to five million cords of pulp wood per year, involving the cutting over of several million acres to furnish it. An im mense source of supply is available from the lumber industry, which wastes more than half of the cut of timber. Much of this is available for paper under more enlightened methods. Many raw materials for the manufacture of paper have been proposed and in other coun tries other materials are availed of. Esparto, a grass growing in southern Spain and northern Africa, is used in England and on the Conti nent. The Japanese use mulberry fibre. Bam boo is also used, although the knots give trou ble. Corn stalks, rice and flax straw, cotton stalks and wild bananas have been tested with varying degrees of success. It is also pro posed by the dehydration of sugar cane at the plantation to extract the raw sugar in temper ate climates and use the cane for making paper, for which it is well adapted. This is now used for fuel in the tropical sugar centres. On the other hand, nothing so economical and con venient as spruce wood has thus far been found for making paper pulp, provided always there is enough of it at hand.