1171. 'Phosphoric acid has been found in the ashes of all plants hitherto examined, and always in combination with alkalies or alkaline earths. By burning the seeds of wheat, rye, maize, peas, beans, and lentils, ashes are obtained quite free from carbonic acid, and consisting entirely of phosphates, with the exception of very small quantities of sulphates and of chlorides.' (Liebig's Chemistry, p. 121.) Plants obtain their phosphoric acid from the soil, and it is a constituent of all land capable of cultivation.