Attempts to make ultramarine artificially would naturally be based on the analysis of the natural product. The following comparison of the compositions of natural and artificial ultramarines shows how nearly the artificial product approaches the natural:— NATURAL ULTRAMARINE. Clément and Desormes. Gmelin. Silica 35·8 per cent. 47·31 per cent. Alumina 34·8 ” 22·00 ” Soda 23·2 ” 12·06 ” Lime 3·1 ” 1·55 ” Sulphuric acid —— ” 4·68 ” Sulphur 3·1 ” 0·19 ” Water and organic matter —— ” 12·21 ” ARTIFICIAL ULTRAMARINE. +------------------------------------------------------------------+ | | Blue. | Green. | +-------------+------------+------+--------+-----+-----------------+ | Observer. |Warrentrapp.|Elfen.|Brunner.|Pohl.| Gentele. | | | | | | | | | Silica | 45·60 | 40·0 | 32·54 |36·67|} 47·31 | | Alumina | 23·31 | 29·5 | 25·25 |32·12|} | | Soda | 21·47 | 23·0 | 16·91 |21·45| 39·93 | | | | | | |(sodium silicate)| | Potash | 1·75 | —— | —— | —— | 3·92 | | Lime | 0·02 | —— | 2·38 | —— | 1·13 | | Sulphuric | | | | | | | Acid | 3·83 | 3·4 | —— | 2·08| —— | | Sulphur | 1·69 | 4·1 | 11·63 | 7·22| 6·62 | | Iron | 1·06 | 1·0 | 2·25 |trace| 1·95 | | | | | | |(ferric silicate)| | Water | —— | —— | —— | —— | —— | | Oxygen | —— | —— | 9·04 | 0·58| —— | +-------------+------------+------+--------+-----+-----------------+ I. Szilasi found three samples of green ultramarine to have the following composition:— Water 2·20 1·20 1·19 Aluminous residue 1·80 1·42 1·41 Silica 16·73 17·18 16·74 Aluminium 15·92 15·87 16·15 Sodium 18·42 18·18 18·10 Sulphur 7·19 6·97 6·85