E.—lo.

In the above table of analyses the phosphoric anhydride is given separately, and the proportion of tricalcic phosphate to which it is equivalent is given in the next column. This has been done as in some cases a portion of the phosphoric anhydride in these guanos is in the form of soluble phosphates of the alkalies, which gives it an increased value. Superphosphate of Lime. The chief objection to raw phosphates, such as bones, phosphatic guanos, &c, is that they require considerable time to decompose in the soil before they become available for the purposes of plant growth. In superphosphates this objection does not exist, since the phosphates have been rendered soluble by the use of sulphuric acid. The chemistry of the process may be expressed as the conversion of the insoluble tricalcic phosphate by the action of sulphuric acid into the soluble monocalcic phosphate and sulphate of calcium or gypsum. Superphosphate of lime is therefore essentially a mixture of monocalcic phosphate and calcium sulphate, together with any tricalcic phosphate that has not been so acted on by the sulphuric acid, and any organic matter, silica, &c, that may have been present in the raw phosphate. The quality of the resulting superphosphate will therefore mainly depend on the nature of the raw material from which it is made. Mineral phosphates that are rich in phosphoric acid will, if properly manufactured, produce high-class superphosphates, while substances poor in this constituent will produce superphosphates with a low percentage of monocalcic phosphate and a relatively high percentage of other substances which were either present in the original substance or which have been formed by the action of the sulphuric acid. For this reason it is not possible to manufacture high-class superphosphates from bones in good mechanical condition. In the first place, the proportion of tricalcic phosphate is not sufficient; and, secondly, if the whole of the phosphate were converted, there is not sufficient calcic sulphate formed to thoroughly dry the mixture. Calcic sulphate has an important influence in this respect on the mechanical condition of the manure. When first made superphosphates are of a pasty consistency, but the calcic sulphate unites chemically with the water in the same way that plaster of Paris (which is the same substance) sets to form a dry mass that is easily broken down to a fine powder. Table V. gives the results obtained with imported superphosphates examined here, and Table VI. those of the New-Zealand-made article.

Table V. — Analyses of Imported Superphosphates.

8

I- % a 8 Districts received from. 9 B CO 'o cfl-£ n i S6 o M ill pH O en ■5.25 ill 02 d 5 O Moneyvalue per Ton. 9 13 49 56 122 123 144 151 154 243 258 399 405 453 578 514 College farm Invercargill College farm Christchurch Auckland Christchurch Lincoln Hororata St Andrews .. 12-40 17-20 6-GO 29-40 .. 14-20 ]0-13 1-60 30-02 .. 15-85 17-14 1-95 25-98 .. 12-55 7-69 1-07 I 29-66 .. 11-00 13-91 1-60 34-27 .. 11-75 6-76 1-15 32-38 .. 17-21 13-25 1-74 2684 .. 10-39 17 26 1-15 31-64 .. 14-18 7-24 6-62 18-11 .. 11-46 7-13 3-70 21-75 3-90 12-91 5-12 32-63 .. 15-67 6-21 2-30 24-73 .. 12-90 4-10 2-74 | 23-40 .. 12-30 4-82 3-02 23-07 .. 13-70 5-83 5-30 21-09 7-52 15-03 5-00 9-30 .. 13-37 18-96 8-32 12-19 12-40 14-20 15-85 12-55 11-00 11-75 17-21 10-39 14-18 11-46 3-90 15-67 12-90 12-30 13-70 7-52 13-37 17-20 30-13 17-14 7-69 13-91 6-76 13-25 17-26 7-24 7-13 12-91 6-21 4-10 4-82 5-83 15-03 18-90 39-83 1-26 .. 32-30 39-77 1-70 1-20 37-17 ! 34-55 2-24 4-70 28-85 > 39-26 2-18 2-05 40-71 ! 45-20 0-43 1-45 34-51 ! 42-90 3-63 2-75 41-39 I 35-55 G-84 6-84 26-72 I 41-76 0-43 3-50 33-72 23-97 6-00 2-30 44-81 28-79 1-00 3-70 51-88 43-20 0-43 1-70 38-42 32-76 Nil 5-40 45-59 30-88 1-31 G-30 4738 30-56 3-49 5-90 47-42 27-92 Nil 3-20 49-46 12-32 9-08 8-30 44-30 16-09 5-67 6-40 34-45 82-30 37-17 28-85 40-71 34-51 41-39 26-72 33-72 44-81 51-88 38-42 45-59 47-38 47-42 49-46 44-30 34-45 1-40 3-98 3-02 4-09 2-77 0-19 0-56 1-91 0-74 0-38 4-89 0-10 1-87 0-48 1-42 1-47 064 I £ b. d. 1-40 0-14 j 8 14 9 398 0-19 ! 9 1 0 3-02 007 7 17 0 4-09 039 9 3 6 2-77 0-06 10 1 6 0-19 0-42 10 0 0 0-56 0-61 8 10 9 1-91 335 9 11 6 0-74 0-19 6 10 0-38 0-05 7 10 4-89 0-08 9 14 3 0-10 042 7 19 0 1-87 0-05 7 10 0 0-48 0-05 7 8 3 1-42 0-19 6 16 6 1-47 1-02 4 7 0 0-64 0-70 4 13 0 747 748 749 759 765 767 768 • 769 Christchurch Rangitikei Geraldine Timaru Temuka 13-29 1-56 : 24-93 14-23 1-60 I 24-93 18-47 0-18 ; 25-25 27-92 6-60 i 18-36 8-84 6-28 ! 25-91 10-57 1-68 | 25-58 11-42 8-54 i 18-36 14-86 6-48 | 24-92 ! ■— r 33-03 j 1-74 5-20 53-: 33-03 0-87 6-60 51 J 33-45 1-30 2-10 52-' 24-32 4-36 4-00 36-' 34-33 7-41 4-98 46". 33-89 1-31 5-30 55-; 24-32 3-92 2-90 54-1 33-02 3-05 4-00 46-1 !8 0-11 8 0 0 ri 005 7 18 fO 0-02 7 18 • )6 0-81 6 7 6 >8 0-08 8 5 3 >6 005 8 3 3 J6 0-08 6 3 0 >9 0-08 7 17 0 !8 7 rO )6 18 i6 !6 >9 11 400 750 College farm Christchurch Bone Superphospkai .. 13-75 18-02 9-55 17-13 .. 12-35 23-75 8-50 16-15 3?75 5-74 15-41 !«s. 22-78 2-62 i 3-50 34-47 21-31 3-93 j 3-00 31-18 20-41 1-74 4-30 88-'( C-96 0-72 6 16 1-14 1-12 6 2 0 16 1-48 6 10