The Duke of Northumberland has made a liberal donation of £25 to the Agricultural Chemistry Association of Scotland.   Sir James GRAHAM has also given a subscription of £2 annually to the same association.  Professor JOHNSTON, of Durham, the chemist appointed by the association, has commenced operations, and has taken commodious premises in Bank-street, Edinburgh, where he has a laboratory, and is now busily engaged in the work of analyzing soils, manures, &c., submitted to him by the members of the association, for his advice and opinion as to their fertilizing properties and capabilities for the successful growth of different crops.