From this it appears that the quantity of acid dissolved increases with the temperature of digestion with the exception of the number obtained at 50°. When the time of digestion was increased there was also found a progressive increase in the amount of acid passing into solution. At 40° for forty-five minutes the per cent dissolved was 4.97, and at 40° for one hour it was 5.92. These early determinations had the effect of calling attention to the thoroughly empirical process which was in use, in many modified forms, by agricultural chemists, the world over for determining so-called reverted phosphoric acid in fertilizers. Since the publication of the paper above named many investigations have been undertaken by Huston and others relating to this matter.[111] The general results of these studies, tabulated by Huston, are given below.[112] INFLUENCE OF THE TIME OF DIGESTION. (A) = Temperature, degrees C. (B) = Citrate-soluble phosphoric acid. (C) = Total phosphoric acid. Material. Authority. (A) Time of (B) (C) digestion. Per cent. Per cent. Bone meal, F. B. Dancy, { 65 ½ hour 10.60 19.75 { 65 1 “ 11.28 19.75 Orchilla F. B. Dancy, { 65 ½ “ 6.62 21.68 guano, { 65 1 “ 6.85 Navassa F. B. Dancy, { 65 ½ “ 4.64 31.27 rock, { 65 1 “ 4.81 31.27 Navassa F. B. Dancy, { 65 ½ “ 9.00 11.47 superphos., { 65 1 “ 9.21 11.47 Bone meal, H. A. Huston, { 40 ½ “ 4.01 20.28 { 40 1 “ 5.92 20.28 Bone meal, H. A. Huston and { 65 ½ “ 6.17 23.58 raw, W. J. Jones, Jr., { 65 1 “ 6.49 23.58 { 65 2 hours 8.22 23.58 { 65 5 “ 9.31 23.58 Steamed H. A. Huston and { 65 ½ hour 10.59 27.67 bone, W. J. Jones, Jr., { 65 1 “ 12.21 { 65 2 hours 14.61 { 65 5 “ 17.94 { 65 10 “ 19.73 Florida H. A. Huston and { 65 ½ hour 0.56 19.75 soft rock, W. J. Jones, Jr., { 65 2 hours 1.69 { 65 5 “ 1.47 Precipitated H. A. Huston and { 65 ¼ hour 26.72 33.34 calcium W. J. Jones, Jr., { 65 ½ “ 27.26 phosphate { 65 1 “ 27.28 from glue { 65 2 hours 27.29 works,