320 Proceedings of the British Association. 



mode of restoring to the land its original fertility. If the theory 

 suggested by the author be the true one, it will follow, that the 

 proper remedy would be, not to discontinue the use of the ni- 

 trates, but by the application of bone manure, &c. at intermediate 

 periods, to restore to the land those other ingredients which had 

 been abstracted from it in too large a quantity. To determine 

 what materials are wanting, and in what proportions they ought 

 to be applied ; (independently of the empirical plan of ascertain- 

 ing, by repeated trials, the substances, which, by their addition 

 succeed best in remedying the deficiency,) two methods present 

 themselves. The first, a difficult one, is to learn by a minute 

 analysis of the soil, whether the ingredients which the crop re- 

 quires are actually present, and to add of these a quantity equal 

 to that which the intended crop is calculated to contain. The 

 second, a more practical scheme, is to estimate in the first place, 

 how much of these substances exists in the crop taken off the 

 ground, and then to add to it at least an equivalent quantity of 

 manure. The Doctor suggested, that in farming establishments, 

 a kind of book-keeping should be undertaken, on this principle : 

 a debtor and creditor account being made out of the quantity of 

 nitrogen, of earthy phosphates, of alkali, &c. abstracted in the 

 form of crop, and restored in that of manure each year. He 

 concluded by specifying certain points relative to this subject 

 which require further investigation. 1. To confirm or disprove 

 his theory, with respect to the operation of the nitrates, by deter- 

 mining whether they actually diminish in quantity, and finally 

 disappear after several successive crops have been grown upon 

 land impregnated with these salts. 2. Whether the same applies 

 to common salt and other mineral manures as to the nitrates, or 

 whether any of them act directly as stimuli. 3. More extended 

 and exact data relative to the amount of alkaline and earthy salts, 

 and of nitrogen present in the various crops cultivated by the 

 farmer, as well as in the manures he employs. 



A practical method of determining the quantity of real Indigo 

 in the Indigo of Commerce, by Dr. Samuel L. Dana, of Lowell, 

 Mass. U. S. A. Dr. D. directs that 10 grains of indigo reduced 

 to an impalpable powder should be boiled in a Florence flask a 

 few minutes, in 2| oz. of a solution of carbonate of soda, mak- 

 ing 30^ to 35° on Twaddel's hydrometer; then add 8 grains of 

 crystals of muriate of tin, and boil for half an hour : a beautiful 



