222 THE WASTE AND CONSERVATION OP PLANT FOOD. 



of soda, iodine, and bromine. The gelatinous portions of seaweeds 

 become exceedingly hard and elastic upon being dried, and have been 

 moulded into various forms as substitutes for horn and shells in making 

 handles for knives, files, and other tools. In the Techno-Chemical 

 Receipt Book, on page 177, may be found receipts for making artificial 

 ebony from the charcoal obtained from seaweeds, also for making 

 leather, soap, and glue. For the latter i)urpose the plants are dried 

 and powdered, extracted with warm water, with or without the addition 

 of alcohol. The solution is allowed to settle at a temperature of iL'O^ F. 

 When cool it forms a jelly, which is used for various purposes. Tlie 

 direction is then given for making trans[)arent seaweed leather, opaque 

 seaweed leather, seaweed soap, and seaweed glue. * 



ISTo attempt can be made to give the quantities of seaweed which are 

 annually cast upon the shores of the different continents. Perhaps 

 Ehode Island is no more favored in this respect than any other locality, 

 and we have seen the value of the seaweed which w-as gathered for 

 agricultural purposes in that State alone. The amount gathered rep- 

 resents only a very small fraction of the amount which was thrown 

 upon the shores. It is easy therefore to conclude that the quantities 

 of nitrogen, phosphoric acid, and i)otash annually removed from the 

 seas by the plants living therein are no less great in magnitude than 

 those removed from the land by crops and plants of all kinds. 



But seaweed and other vegetable products of the sea are not the 

 only vehicles in which the plant food in solution in the waters of the 

 ocean may be returned to the uses of man. The animal life of the ocean 

 is not less important than that of the land. In the aninuil economy of 

 the ocean are gathered, therefore, immense quantities of valuable food 

 material which are thus placed in a condition to be at least in part 

 restored in the form of food. Relatively, i)hosplioric acid and nitrogen 

 are restored in much greater quantities than potash. The composition 

 of fish in general shows that relatively larger quantities of phosphoric 

 acid and nitrogen are found than of fat and potash. The chemical 

 composition of the nutritive portion of fishes has been thoroughly 

 investigated by Atwater.^ 



The percentage of i)hosphoric acid in the flesh of American fishes in 

 its fresh state is about one-half of 1 per cent. In one instance, that of 

 smelt, Atwater found 0.81 per cent in the flesh of the fish. In the water- 

 free substance of the flesh the percentage of phosphoric acid in round 

 numbers is 2.5. In the case of the smelt, above mentioned, it amounted 

 to 5.19 per cent. When it is considered that the bones and other refuse 

 of the fish, presumably richer in phosphoric acid than the flesh, were 

 Bot included in this investigation, tlie (luantity of phosphoric acid in 

 fish is distinctly brought to view. 



"'The chemical composition and nutritive values of food fish and ac<iua.tic Ver- 

 tebrates," by W. O. Atwater. Eeport of the United Stateti Commissiouer of Fish 

 and Fisheries 1888, pages 679-868. 



