April 29, 1922] 



NATURE 



543 



and flow-sheets, the detailed sketches of parts and of 

 special devices, and the examples of methods of 

 statistical control, constitute a body of information 

 of a unique character. The description forms a 

 permanent record of these matters in a connected 

 narrative, but again its usefulness is by no means 

 confined to the explosives manufacturer, since many 

 of the methods used and devices for overcoming 

 difficulties are subject-matter for numerous projects 

 in chemical engineering. 



Concentration of Sulphuric Acid. — In the third 

 volume will be found a useful study of the thermal 

 conditions obtaining in the Gaillard tower system. 

 The methods used before the war in this country for 

 concentrating the sulphuric acid of 70 per cent, strength 

 resulting from processes of nitration were for the 

 most part the Kessler and the cascade systems, both 

 of which are operated with comparatively small units. 

 Excellent results both as regards efficiency and low 

 cost of working were obtained with the large Gaillard 

 towers erected in the large explosives factories such 

 as Queen's Ferry and Gretna, The feature of these 

 towers is the conversion of the weak acid into a spray, 

 which in falling by gravity down a tower of about 

 50 ft. in height, meets ascending hot gases from a 

 producer, and so becomes concentrated to a strength of 

 92-95 per cent, sulphuric acid. As the fuel consump- 

 tion, weight of dilute acid, and weight of concentrated 

 acid can be measured with fair accuracy, the oppor- 

 tunity is taken to calculate the efficiency of the plant 

 from a knowledge of the various thermal data available, 

 including those of Porter for sulphuric acid and oleum. 

 The various factors are considered in detail which 

 will repay the study of technical students, and a 

 satisfactory heat balance is made out in which the 

 heat imported into the system is contrasted with 

 that which is lost by water evaporating, by radiation, 

 and by being carried away in the hot acids. As the 

 last-mentioned source of loss amounts to nearly a 

 quarter of the heat put into the system, its recovery 

 on counter-current lines by suitable constructional 

 modifications would appear to be worth attempting. 



A short study follows of the Gilchrist concentrating 

 plant, which worked on a process analogous to that 

 of the Kessler plant, but with a high capacity. 



It had been a disadvantage in all the varieties of 

 concentrating plant mentioned that the gases finally 

 discharged into the air carried with them a mist of 

 dilute sulphuric acid in water, involving a certain 

 loss of acid and considerable inconvenience to those 

 working in the neighbourhood. It was also objection- 

 able in explosives factories where many large-scale 

 operations have to be conducted in an acid-free atmo- 

 sphere. Accordingly it was determined to precipitate 



NO. 2739, VOL. 109] 



this mist electrically by the Cottrell electrostatic process, 

 of which full details are given and also a description of 

 all the electrical parts and their mode of maintenance. 

 As about 3 per cent, of the acid fed into the concen- 

 trating plant was recovered in the Cottrell precipitating 

 plant, it will be seen that besides the advantages 

 mentioned, a useful addition to the yield of acid was 

 obtained. 



Acid Mixing. — In No. 4 of this series is described 

 the working of that important section of a nitration 

 factory in which the acids are adjusted as regards 

 their quantity and composition. In such a factory 

 as Queen's Ferry, where 700 tons of trinitrotoluene 

 a week could be made, the magnitude of the problems 

 of production, handling, and conveyance of acids 

 may be judged from the vast quantities — about 43,000 

 gallons — of nitric and sulphuric acids occurring in 

 many stages of dilution. It is essential to secure 

 that the various acids are in balance for controlling 

 the cycle of production and recovery in manufacture. 

 An example for a given output of explosive is worked 

 out, and a diagrammatic acid balance figured, which 

 includes a set of factors by which the quantities of 

 acid at various stages must be modified to compensate 

 for variations in working of the units composing the 

 acids cycle. In this way the proper quantity of mixed 

 nitrating acids of a definite composition and the 

 economical utilisation of spent acids are kept under 

 strict control. 



As variations in dilution and in strength of the 

 concentrated sulphuric and nitric acid inevitably 

 creep in, calculations must be made of the adjust- 

 ments necessary to bring the contents of the large 

 mixing vessels to the desired composition. The 

 methods for doing this are explained, and it is of 

 interest to note that the presentment of the necessary 

 data in the form of graphs was abandoned in favour 

 of a series of simple tables by means of which the 

 necessary additions for obtaining a correct mixing 

 could be found. 



A description is given in detail of the plant for 

 storing and mixing these acids, and this completes 

 the account of the manufacture of trinitrotoluene 

 contained in vol. 2. 



Apart from its value as an exposition of scientific 

 method applied to the control of acid mixing for a 

 nitration process on the largest scale, there will be 

 found other subject-matter, such as descriptions of 

 the mechanical details, methods of controlling undue 

 rise of temperature, prevention of wear of parts, and 

 methods of distribution of acids by pipes, which will 

 be found to have a wide interest among those con- 

 cerned with the erection of plant. 



It is clear that the publication of the data which 



