The preparation of the solution is effected by adding the sulphur to boiling sulphide of sodium liquor of maximum strength until it ceases to be taken up. The clay and soda are first roasted together at a red heat, so as to effect a partial double decomposition, and the product, after grinding, is made into a thick paste with “sulphur liquor,” i. e. the sulphide of sodium solution of sulphur. This latter operation may be carried out in an ordinary pug-mill. The paste so formed is dried in an oven or other convenient way, and the dried mass (being broken into small pieces) is roasted without access of air in a closed earthenware retort, first at about 480°-570° F. for an hour, then at a red heat for eight hours, and finally at a moderate heat just below dull redness, in presence of a slow current of air, which enters through a series of holes or small openings in the front of the retort, the current being regulated by means of a damper or an adjustable slide. The retort should be allowed to become quite cold before being opened, otherwise the tint of the product will be injured. McIvor has found the following proportions of the raw materials used in the process to yield excellent results, viz:-- Sulphide of sodium 42 lb. Sulphur 20 “ Kaolin (china clay) 110 “ Soda (as carbonate) 106 “ or Caustic soda 40 “ These quantities yield about 2 cwt. of ultramarine blue. The following communication from the pen of J. B. Nejedly, of Vienna, appeared in the _Chemiker Zeitung_, during 1888:-- “Animated by various articles and notes in your journal under the heading of ‘The Present Position of the Manufacture of Ultramarine,’ I would like to draw out of obscurity a little work on this industry which contains much that is true, and furnishes at the same time many comparisons with regard to the present position of the ultramarine industry in Germany. “The work above referred to was printed in the year 1840 and bears the title:-- “‘Treatise on the chemico-technical preparation of Ultramarine colours, according to the discoveries of Leykauf and Heyne, or on the importance of the manufacture of blue and green Ultramarine for purposes of science, art, and industry. By Friedr. Wilh. Heyne, president of the Nürnberg Ultramarine Manufactory. Nürnberg: 1840. Printed at the Campe Press.’ “The preface, which I consider to be well suited to present circumstances, I reproduce verbatim, while from the little work itself I will only quote such sentences as would seem to be suited to the present time, and which are the most important as bearing on the subject.