With respect to the feeble acid energy of boric anhydride I think it useful to add the following remarks. Carbonic anhydride is absorbed by a solution of borax, and displaces boric anhydride; but it is also displaced by it, not only on fusion, but also on solution, as the preparation of borax itself shows. Sulphuric anhydride is absorbed by boric acid, forming a compound B(HSO_{4})_{3}, where HSO_{4} is the radicle of sulphuric acid (D'Ally). With phosphoric acid, boric acid forms a stable compound, BPO_{4}, or B_{2}O_{3}P_{2}O_{5}, undecomposable by water, as Gustavson and others have shown. With respect to tartaric acid, boric anhydride is able to play the same part as antimonious oxide. Mannitol, glycerol, and similar polyhydric alcohols also seem able to form particularly characteristic compounds with boric anhydride. All these aspects of the subject require still further explanation by a method of fresh and detailed research. [6] Ditte determined the sp. gr.:-- 0° 12° 80° B_{2}O_{3} 1·8766 1·8470 1·6988 B(OH)_{3} 1·5463 1·5172 1·3828 Solubility 1·95 2·92 16·82 The last line gives the solubility, in grams, of boric acid, B(OH)_{3}, per 100 c.c. of water, also according to the determinations of Ditte. [7] It is evident that, in the presence of basic oxides, water competes with them, which fact in all probability determines both the amount of water in the salts of boric acid as well as their decomposition by an excess of water. In confirmation of the above-mentioned competing action between water and bases, I think it useful to point out that the crystallo-hydrate of borax containing 5H_{2}O may be represented as B(HO)_{3}, or rather as B_{2}(OH)_{6}, with the substitution of one atom of hydrogen by sodium, since Na_{2}B_{4}O_{7},5H_{2}O = 2B_{2}(OH)_{5}(ONa). The composition of the acid boric salts is very varied, as is seen from the fact that Reychler (1893) obtained (Cs_{2}O)3B_{2}O_{3}, (Rb_{2}O)2B_{2}O_{3} (corresponding to borax) and (Li_{2}O)B_{2}O_{3}, and that Le Chatelier and Ditte obtained, for CaO, MgO, &c., (RO)B_{2}O_{3}, (RO)_{2}3B_{2}O_{3}, (RO)2B_{2}O_{3}, (RO)_{2}B_{2}O_{3}, and even (RO)_{3}B_{2}O_{3}.