TRANSACTIONS OF THE SECTIONS, 61 



we canuot produce artificiallj^, and without which we cannot exist. The quantity 

 of madder grown in all the madder-growing countries of the world prior to 1868 

 was estimated te be 70,000 tons per annum ; and at the present time the artificial 

 colour is manufactured to an extent equivalent to 50,000 tons, or more than two 

 thirds of the qiumtity grown when its cultivation had reached its highest point. 



I might have referred to other subjects besides the coal-tar colours which have 

 resulted from scientific research ; but I know of no otlier of such interest and 

 magnitude. From the brief history I have given, we see that the origin of these 

 colouriug-matters is entirel}' the fruit of many researches made quite independently 

 by different chemists, who worked at them without any knowledge of their futm-e 

 importance ; and on looking at the researches which have thus culminated in this 

 industry, it is interesting to notice that many, if not most of them, were conducted 

 for the purpose of elucidating some theoretical point. 



These facts certainly ought to be a great encouragement to chemists, and stimu- 

 late them to greater activity. It woiUd be very pleasing to see more work ema- 

 nating from the chemical schools of the United Kingdom ; and I think no student 

 should consider his chemical curriculum finished until he has conducted an original 

 research. The knowledge obtained by a general course of instruction is of course 

 of very great value ; but a good deal of it is earned on by rule. In research, how- 

 ever, we have to depend upon the exercise of our judgment, and, in fact, of all our 

 faculties ; and a student having conducted even one, under the guidance of an 

 efficient director, will find that he has acquired an amount of experience and 

 knowledge which will be of the greatest value to him afterwards. 



It is hoped these remarks will encourage young chemists to patiently and 

 earnestly work at whatever subject they may undertake, knowing that their results, 

 although sometimes apparently only of small interest, may contain the germ of 

 something of gi-eat scientific or practical importance, or may, like a keystone in 

 an arch, complete some subject which before was fragmentary and useless. 



On a Safe and Rapid Evaporating-]}an. By P. H. T. Allan. 



In the course of various chemical manufactui-es there is sometimes met the diffi- 

 culty of products and apparatus being injured or destroyed in the process of rapid 

 evaporation by the salts settling to the bottom of the pan, and there becoming a 

 solid mass. This pan is intended as an effort to overcome that difficulty. 



Besides attempting to compass the evaporation of the leys or other fluids safe 

 from the danger of deposition upon the heating-surface, it also provides for the 

 rapid evaporation of the fluids, with confimwus action in the pan, and the readi/ 

 removal of the solids when formed. To attain these several ends, the form to be de- 

 scribed has been found necessaiy. The pan may be made of boiler-plate, and .about 

 30 feet long, by 10 feet broad, and 9 feet high. The heating-surface is supplied by 

 two flues of a V-shape carried through the fluid from one end of the pan to the 

 other. Tlie acutest angle of the V is downward, and within 2 feet of the bottom 

 of the pan. This form of heat-source whilst raising the temperature to boiling- 

 point and effectually keeping it there, offers no resting-place for descending particles ; 

 and consequently the salts on separating fall to the bottom of the pan and there 

 accumulate. Now the apparatus is so an-anged that the bottom slopes in one or 

 more directions ; the salts gather in the deepest parts, and suitable outlets that may 

 be closed at pleasure being provided in the sides, they gi-avitate outwards into 

 proper receptacles. Care must be taken that sufficient solids are left in to occupy 

 the outlets, and the passage of fluids thereby prevented. 



The upper part of the X -shaped flue is covered in its whole length and breadth 

 by an air-chamber of iron fitted with pipes or other arrangement passing into the 

 liquid, whereby the air heated from the waste heat of the flue is forced into the 

 boiling liquid, and there materially increases the rapidity of the evaporation. 



For the purpose of utilizing any heat that may escape from the air-chamber a 

 small pan occupies its upper surface. On this subsidiary pan the liquid may be 

 boiled to nearly saltintj-point. and then allowed to flow into the salting-down pan, 



1870. ^ ' 6 



