December 9, 1922] 



NA TURE 



779 



the more familiar form of platinised asbestos, was 

 also taken over and worked at H.M. Factory, Pembrey. 

 The Mannheim and Tentelew plants were constructed 

 to burn iron pyrites ; in the large Grillo plants, sulphur 

 was burnt, among other reasons, in order to reduce the 

 size of the towers used to purify the gases. This 

 purification has been from the beginning the most 

 essential feature in the successful manufacture of 

 sulphuric acid by the contact process, and is substanti- 

 ally the same in all the different systems. It was, 

 however, found that, even after the most careful 

 purification of the gases, the proportion of sulphur 

 dioxide converted to the trioxide was lower in the 

 Mannheim and Tentelew plants than in the Grillos, 

 where the efficiency often reached 94 per cent, instead 

 of something less than 90 per cent. 



While, however, the report describes in detail many 

 elaborate technical features which were essential in 

 order to secure high yields and efficiencies, it is of 

 interest to find that the apparently simple operation 

 of burning the pyrites provided an opportunity for 

 securing improved yields, that may be compared in its 

 simplicity with the washing of nitre bags, since it was 

 found that careful attention to the method of building 

 up and raking the fires resulted in the reduction of 

 the sulphur content of the spent ore from 8 to 2 per 

 cent. This feature proved to be so important that, 

 in addition to an accurate time-table specifying 

 exactly when the fires were to be raked, charged, and 

 dropped, there was actually drawn up at the Queen's 

 Ferry factory a chart to show exactly how the prong 

 of the rake should be dragged or pushed through the 

 fire in order to produce the best results, and this 

 diagram is regarded as of sufficient importance to be 

 reproduced in the report. The report also contains 

 a precise specification of the way in which the fire- 

 bars must be moved in order to remove the burnt 

 pyrites from the furnace. It was by attention to 

 such details as these that the high efficiencies 

 ultimately achieved in the different factories were 

 reached. 



Perhaps one reason why chamber plants did not 

 receive more attention was that, even when T.N.T. 

 could be manufactured without oleum, it was still 

 found to be advantageous to supply in this form the 

 sulphuric acid required to make up for the losses 

 sustained during working, e.g., in the form of fumes 

 and in the various washing waters, since in this way it 

 was possible to avoid the final stage in the concentration 

 of the sulphuric acid, e.g., from 92 to 96 per cent., 

 which was also the most expensive and the most 

 wasteful part of the process. 



Picric Acid. 



The manufacture of picric acid presented a third 

 type of problem. At the beginning of the war 

 this acid was the only approved filling for H.E. 

 shells, for Land Service as well as for the Navy. 

 The demand for the acid soon outstripped the available 

 supplies of coal-tar phenol, and it therefore became 

 necessary to make use of coal-tar benzene as the raw 

 material. This could" be converted into picric acid by- 

 passing either through monochlorobenzene and dinitro- 

 chlorobenzene or through sodium benzenesulphonate 

 and synthetic phenol. In this country the latter 



NO. 2771, VOL. I I o] 



priM ess was adopted almost exclusively. In France 

 the chlorination process was also used, although in 

 many cases the manufacture was arrested at the pen- 

 ultimate stage of dinitrophenol — a milder explosive, 

 which gave rise to many fatalities before its toxic 

 properties were realised and controlled with the help 

 of proper physiological tests. 



The manufacture of synthetic phenol lends itself 

 to considerable variations in plant and process, and 

 the sixth report contains diagrams illustrating five 

 different variations worked out by different manu- 

 facturers. The subsequent conversion of the phenol 

 into picric acid also included a considerable range of 

 variants, which are set out fully in the report. It 

 may, however, be of greater interest to refer briefly 

 to the final chapters of the history of picric acid manu- 

 facture, in which the personal influence of the late 

 Lord Moulton was a dominating feature. Convinced 

 from a very early date that vast quantities of explosive 

 would be required, he had laid down as a fundamental 

 proposition the view that these could be obtained only 

 by using ammonium nitrate as the main basis of the 

 shell-filling programme. In this connexion the limited 

 supplies of T.N.T. were of particular value, since this 

 compound could be diluted with ammonium nitrate 

 to five times its original weight, and even then gave 

 an explosive mixture which was of greater power 

 than, although not quite so violent as, T.N.T. or picric 

 acid. The insensitiveness of this mixture, which 

 ultimately became one of its most valuable properties, 

 made it very difficult at first to secure effective detona- 

 tion, and a maximum output of picric acid was there- 

 ' fore demanded in order to secure complete detonation 

 of the largest possible proportion of shells. Many 

 efforts were made to dilute picric acid in the same way 

 .as T.N.T., and in France (where picric acid was adhered 

 to until the end of the war, in spite of its high cost) 

 it was diluted with a wide range of other nitro-bodies ; 

 but the dilution of ammonium picrate with ammonium 

 nitrate was never sufficiently successful to provide a 

 service filling. 



When, therefore, the detonation of the mixture of 

 T.N.T. and ammonium nitrate had been improved 

 until its equality with picric acid was at last established, 

 there was no reasonable alternative but to abandon 

 altogether the use of this acid, which cost three times 

 as much, and, moreover, required nearly eight tons of 

 imports, instead of less than two tons, in order to give 

 one ton of finished explosive. Very severe criticism 

 was levelled against Lord Moulton's action in spending 

 more than a million pounds in erecting a factory for 

 the manufacture of picric acid, which was abandoned 

 almost as soon as it was finished ; but this criticism 

 was really only a proof of the ignorance of the critics, 

 since the policy on which it was based was one that 

 effected a saving of several million pounds per year, 

 in addition to effecting a reduction of imports which 

 was at the time of vital importance. In this, as in 

 other problems, Lord Moulton saw clearly almost 

 from the beginning what must be done to achieve 

 success, and the closing down of the Avonmouth factory 

 was the final vindication of the policy which he had 

 adopted, and then followed persistently, in spite of all 

 the obstacles that it had to encounter, until he had 

 accomplished his purpose. 



