AQUATIC TRODUCTS AS FERTILIZERS. 275 



wliicli can be expelled by burning. Since grinding docs not reduce 

 the material to so fine a state as burning does, the ground shell is 

 not so active chemically. 



The most popular manner of utilizing shells is to burn them and 

 slack the product with water. The slacking may be done in heaps 

 covered with moistened earth, and the fine powdery hydrate of lime 

 spread directly upon the land; or the lime may be used in the com- 

 post heap; or the quicklime maybe left to become air-slacked by 

 exposure to the air, and the product be applied to the land instead 

 of leached ashes. 



AQUATIC PLANTS AS FERTILIZERS. 



Although it does not appear that the many properties of aquatic 

 plants have been fully exploited, their uses are far more numerous 

 and diversified than is generally supposed. Their most widely known 

 economic value is as furnishing tliousands of tons of fertilizer and a 

 great variety of nutritious and wholesome foods. In addition thereto, 

 they are utilized in the production of many chemicals, especially 

 iodine and bromine, and as a constituent in glues and gelatines, and 

 as a basis for trade fruit-jellies. They also serve in sizing fabrics, in 

 refining beer, as a mordant in dyeing, as composition in cement for 

 covering boilers, for stufftng upholstery, jiacking porcelain, in making 

 paper, fishing-lines, ropes, buttons, handles for cutlery, as tents in 

 surgical operations, etc. The gathering of seaweeds in Great Britain 

 early in the present century is said to have given employment to 

 about 100,000 persons, the product being used in the manufacture of 

 carbonate of soda. 



On the coasts of France and the British Isles thousands of tons of 

 seaweeds are collected annually for fertilizing tlie crops. In China 

 and Japan they have been used as fertilizer for many centuries, but 

 in recent years the emplojauent of seaweeds for this purpose has been 

 much reduced, owing to their more extended use as food and in the 

 chemical and manufacturing industries. In the New England States 

 they are probably the most important fertilizing material used on 

 those farms immediately adjoining the sea. According to Storer, 

 with the exception of the farms of the Connecticut Vallej^ and those 

 enriched by fish scrap or by manures received from the cities, ' ' the 

 only really fertile tracts in New England are to be found back of 

 those sea beaches upon which an abundant supply of seaweeds is 

 thrown up by storms." In the Middle Atlantic States the use of sea- 

 weeds as fei-tilizer is not so extensive, but in the aggregate very large 

 quantities are employed. Elsewhere in the United States their use is 

 of less importance. 



There are three principal groups of aquatic plants used in this 

 country for fertilizer, viz, rockweeds, kelp, and eelgrass or grass rack. 

 Rockweeds are the large dark-colored plants furnished with smaU 

 bladders or snappers, which constitute at least 75 per cent of the 



