Page:Popular Science Monthly Volume 23.djvu/831

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culm (as the coal-dust is technically called) with pitch into blocks, brick-shaped, weighing but fourteen pounds each. Anything tending to the utilization of what is now waste is of value, when we consider that the amount of anthracite coal sent to market represents but about four fifths of the quantity that is actually raised from the earth, the balance being piled up in unsightly heaps.

Many of the subjects which I have incidentally touched upon have been so elaborately dealt with by specialists in papers before the members of this society, that the ground has been taken from under me, and I am but a gatherer and gleaner, summarizing, as it were, the results of their descriptions. Although, in the period under review, many of the waste products of manufactures, formerly thrown away, have been made to serve a useful purpose, there is yet room for fresh efforts in this direction, and the reward is certain. The manufacturer who discovers a heretofore unknown use for the waste product of his work necessarily cheapens the cost of the principal article of his production, and thus secures an advantage over competitors. Much, as we have seen, has already been done in this way, but there are many other products which could be made under the direction of that mighty converter, chemistry, to yield substances of use and profit.

Science has taught us how to transmute the waste and refuse materials—elements of pollution—into sources of economy and wealth. The utilization of the sewage of great cities for agricultural ends has virtually been a demonstrated success in Paris and many of our own towns. The same success, by patient experiment, is obtainable in many other waste products, which, in ignorance of their value, we suffer to defile our streets, pollute our rivers, and taint the air we breathe. The purification of the outflow of paper-mills and the utilization of the sludge and other waste products are now carried out.

It would have been impossible, in the limits of this paper, to refer in detail to more than a few of the principal examples of the successful use of refuse. But those enumerated will serve to show to how great an extent civilization is daily adding to the useful products of the world, both by economizing its resources and by calling forth new ones with the aid of chemistry.


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SYMBIOSIS AND "VEGETATING ANIMALS."

A REVIEW.

By W. T. SEDGWICK, Ph.D.,

ASSOCIATE IN BIOLOGY, JOHNS HOPKINS UNIVERSITY, BALTIMORE.

SINCE the publication of the interesting observations and speculations of Dr. Karl Brandt concerning the occurrence of chlorophyl in animals, of which a summary account was given in a recent number of this periodical, under the heading "A Partnership of Plant