In 1840 appeared Liebig's _Chemistry in its Application to Agriculture and Physiology_, tracing the relations between the nutrition of plants and the composition of the soil, a book which was received with enthusiasm, and completely changed the attitude which agriculturists generally had maintained towards chemistry; one of contempt, founded on ignorance. But, as Mr. Prothero has said,[621] 'if the new agriculture was born in the laboratory of Glissen, it grew into strength at the experimental station of Rothamsted.' There, for more than half a century, Lawes and Gilbert conducted experiments, of vast benefit to agriculture, in the objects, method, and effect of manuring; the scientific bases for the rotation of crops, and the results of various foods on animals in the production of meat, milk, and manure. The use of artificial manures now spread rapidly; bones, used long before uncrushed, are said to have been first crushed in 1772, and their value was realized by Coke of Holkham, but for long they were crushed by hammer or horse mill, and their use was consequently limited. Then iron rollers worked by steam ground them cheaply and effectively, and their use soon spread, though it was not till about 1840 that it can be said to have become general. Its effects were often described as wonderful. In Cheshire, cheese-making had exhausted the soil, and it was said that by boning and draining an additional cow could be kept for every 4 acres, and tenants readily paid 7 per cent. to their landlords for expenditure in bone manure. Its use had indeed raised many struggling farmers to comparative independence.[622] A very large quantity of the bones used came from South America.[623] Porter also noticed that 'since 1840 an extensive trade has been carried on in an article called Guano', the guana of Davy, 'from the islands of the Pacific and off the coast of Africa'. Nitrate of soda was just coming in, but was not much used till some years later. In 1840 Liebig suggested the treatment of bones with sulphuric acid, and in 1843 Lawes patented the process and set up his works at Deptford.[624] Italian rye grass, not to be confounded with the old English ray grass, had been introduced by Thomson of Banchory, in 1834, from Munich;[625] and though the swede was known at the end of the eighteenth century, in many parts it had only just become common. In Notts it was in 1844 described as having recently become 'the sheet-anchor of the farmer'.[626] In Cheshire a writer at the same date said, 'in the year 1814 there were not 5 acres of Swedish turnips grown in the parish where I reside; now there are from 60 to 80, and in many parts of the county the increase has been in a much greater ratio.'[627]