346 On Sensitisers for Rays of Low Refrangibility. [Mar. 12, 



glass jar, covered with bibulous paper, for seven or eight days, a 

 deposition of the dye in a crystalline state, together with sulphite of 

 calcium, will take place, which latter, owing to its insolubility in 

 water, may be removed by filtration. 



The alizarin-blue S is separated from any unaltered substamv 

 in the original stoppered vessel by solution, and added to the brine, 

 now purified from lime salts, and once more set aside to crystallise, 

 the final purification being effected in a beaker containing alcohol and 

 a small percentage of water to remove the last traces of sodium 

 chloride, collecting the crystals on a filter-paper and drying at 

 ordinary temperatures. 



The needle-shaped crystals are of a deep-red. Dilute solutions am 

 of a pale sherry colour, changing, with the addition of a few drops of 

 ammonia, to a green, which immediately gives way to magenta aifl 

 every shade of purple, till oxidation is complete, when it assumes a 

 blue colour, the absorption spectrum of which is continuous and 

 strongest in the least refrangible end, presenting the appearance of 

 extending into the infra-red. 



Plates immersed in a solution containing 1 : 10,000 and 1 per cenK 

 of ammonia give the most perfect results the day after preparation, 

 but rapidly deteriorate unless kept quite dry. 



With a slit T<yW i nc h i n width, and an exposure of 40 rniuutes, 

 results have been obtained in the region of Great A of the 2nd 

 which possess all the detail and definition usually so characteristic of 

 the violet end. Numerous lines are sharply depicted which were pre- 

 viously not known to exist. X 8400 has been reached, giving almost 

 jqual detail.* 



The process for the preparation of pure ccerulin S is a sli 

 modification of the preceding. The results obtained, as well as the 

 actinic curve, are almost identical. The pure substance is almost 

 white ; dilute solutions pass rapidly from pale yellow to a bright 

 green ; a trace of ammonia produces an olive-green. In general a 

 solution of aurantia as an absorbent in quart/ cell was used. 



For several samples of paste I am indebted to the kindiu 

 Messrs. Schott, Segner, and Co., of Manchester, agents t> 

 Badische Anilin- und Soda-Fabrik, Ludwigshafen, who hold the 

 patent rights for the manufacture of alizarin-blue S. It is hoped 

 this company may be induced to manufacture this substance free 

 from the minute crystallisable impurities which render it unsuitable 

 for use in investigations of such delicate nature. 



* P.S. With a low sun at times screens were found unnecessary. Colonel 

 Water-house, who has also employed alizarin-blue (' Photographic News,' 

 1889), states that Schiendl and Eder failed to recognise the sensitiveness of this 

 substance to the red, and considers that red or yellow screens are required t 

 produce the full effect. 



