6^4 



THE THOPiCAL AGRICULTURIST. tMASCH i, 1887. 



years to season, and it has a perfectly surprising 

 power of absorbing and retaining moisture. Thius 44 

 cwt. 2qr. ot birch were subjected to the test for ninety- 

 four hours, and then examined, when it was found 

 to be completely " seasoned, free from cheeking, rents, 

 or warpiug, and it had given off in the operation 10 

 cwt. 2 qr. 24 lb. weight of water !" Wool so treated, 

 even tested by the microscope, " shows no evidence 

 of any change beyond the dryness of its substance, 

 and this appears uniform throughout," " the fibre and 

 cells seem to be unchanged ; they are as close, but no 

 closer, th»n before, and there is no perceptible shrink- 

 age ot dimension. Some lengths of ash gave still more 

 striking results. Out of 47 cwt. 3 qr. no legs than 21 cwt. 

 1 qr. of moisture was extracted ; 22 cwt. of maho- 

 gany yielded 6 cwt. of moisture in ninty-six hours, 

 whereas to obtain the same result by ordinary 

 exposure would have taken years to accomplish. 

 British oak is a very stubborn wood to reason. Some 

 logs, two inches thick, were finished in nine days, 

 which by natural drying would have required three 

 or four years. These effects were accomplished with 

 a current of 6,200 cubic feet per minute ; and the 

 great lesson they teach is that ail the mischiefs hither- 

 to produced by drying systems accrued from the 

 excessive heat. In this process the temperature never 

 exceeds blood heat ; and as a consequence, delicate 

 fibres, fabrics and chemicals are uninjured. The in- 

 dustrial value of this important discovery can scarcely 

 be over-estimated. A technical journal computes that 

 in the matter of Indian tea alone cool-air drying would 

 probably give it such an advantage as to increase its 

 saleable value £200,000 a year." ('.) So much for Mr. 

 Jennings's process. 



Oomiug now to the Glasgow one, introduced by 

 Messrs. Main and Dick, the former of the well-known 

 firm of A. and J. JNIain and Oo., I cannot ask you 

 for space in this, and the further communication I 

 propose to send you next week, to do more than com- 

 pare its priuciples with those of Mr. Jennings's system, 

 leaving a description of the application of the prin- 

 ciples to a luture occasion. Mr. Main, your readers, 

 will remember, visited India during the Calcutta Ex- 

 hibition, and during his visit travelled considerably 

 among the Tea Gardens, with a view to obtaining a 

 practical insight into the class of iron house.s most 

 suited to the wants af Plaaters, and also to inspect 

 the various applianct-s used in tea manufacture, in 

 the hope of being able to improve upon one or other 

 of these. By conversation with planters he soon 

 learned that in the matter of withering wet leaf in 

 bad weather there was a field practically untouched 

 by inventors. He claims now to have succeeded in the 

 efforts he has been strenuously making since his return 

 to provide the loag-lookeJ for withering appliance, 

 and, whilst engaged upon his research in this direc- 

 tion, to have done even more than he had orginaily 

 sought to do, inasmuch as a modification of the prin- 

 ciple he has adopted for withering, assisted by means 

 of a different appliance and different temperature, 

 has shown him that he can not only wither but " dry " 

 tea also. From start to finish Mr. Main has consulted 

 eminent chemists and practical planters, and has 

 spared no pains or expense in prosecuting his ex- 

 periments, which have been conducted over two 

 years. His process is based upon thoroughly 

 seieutific grounds, and worked out on scientific 

 principles, with every regard for obtainable scien- 

 tific data ; and it is indeed remarkable how 

 identical the resulting principle is with that of Mr. 

 Jennings, although it it true the method of desic- 

 cation varies. The point of difference may bo briefly 

 Stated as follows : — Mr. Jennings desiccates his air by 

 means of heat and then cools his air again ; Mr. 

 • Main desiccates his air by means of an almost ever- 

 lasting absorbant, and saves both the cooling process 

 and certain other disadvantages. 



In considering this matter of rapid and effectual 

 withering and drying, it is as well to seek the fund- 

 amental principles. To solve the problem, IMr. .le.u- 

 nings and Mr. Main, if asked, would probably both 

 refer us to desiccated air, but when asked ho w b est 

 to obtain desiccated air with which to conjure, Mr. 



Jennings would probably reply, by means of super- 

 heating it — I have not asked him — and Mr. Main 

 would answer, by means of an absorbent — I have asked 

 him and cangive his reasons. Possibly Mr. Jennings 

 might be converted to Mr. Main's opinion were the 

 latter's arguments brought to his attention ; but 

 that is surmi.se. Knowing Mr. Main, and being al- 

 ready acquainted with his interest in this subject, in 

 my search after " more light," I brought Mr. Jenning's 

 process to his notice, and it will afford some insight 

 into the thorough and extremely careful manner in 

 which he has conducted his labours if I give the gist 

 of some of his comments upon Mr. Jenning's process 

 as compared with his own. He forwarded me the 

 subjoined table which shows the amount of moisture 

 or water-vapour in the air, per 1,000 cubic feet, at the ' 

 point of saturation, at various temperatures, and he 

 tells me that from such facts as these he was led to 

 wonder, how a delicate substance like tea, could ever 

 be quickly or effectively dried during the rainy sea- 

 son, with so much moisture in the air. Finally he 

 came to the conclusion that the whole of the diffi- 

 cultie s of the process lay in the presence of the ex- 

 cessive moisture in the air — a fact already too well 

 known to planters — and he then felt sure that the 

 reason why so many failures had occurred in machines 

 constructed for drying tea, lay in the fact that moist 

 air — hot though it undeniably was — was used. As soon 

 as he experimented with desiccated air, astounding results 

 were obtained. In drying (not withering) he found that 

 when employing desiccated air a large reduction in the 

 temperature showed more effective results as regards 

 the time occupied, than a high temperature showed 

 when uudesiccated air was used. Thus at a tempera- 

 ture of 200 degree Fahr. rolled leaf was perfectly 

 dried in fifteen minutes ! To practical planters it is 

 unnecessary for me to draw any comparison from 

 this. Mr. Main rightly refuses to express any opinion 

 upon the quality of tea produced at a low temperature, 

 as he is most careful in testing every detail before 

 committing himself to any statement as to its value ; 

 and, as he says, the question of quality cannot be 

 properly settled except by actual experiment with tea- 

 leaf, which cannot be effected in this country. At 

 the snme time, if there be anything in the views I 

 have previously expressed in your columns, I, for one, 

 look forward to improved tea being produced, when 

 rapid firing at low temperatures i> introduced. 



Having taken up so much of your space this week 

 I will, w ith your permission, continue my remarks 

 upon the pnnciple.i of the new process next week.— 

 I am, &c., Aetkmus. 



Table of weights of water in form of vapour capable 

 of being held in suspension by atmospheric air at 

 different te mperatures, the same being dew point or 

 point of greatest saturation: — 



Temp. Fahr. Weight in lb. per 1,000 cubic feet. 

 70 deg. l'li»7 equal, say, 1 lb. 3 oz. 

 1-204 „ 1 lb. Hoz. 



„ 1-275 „ 1 lb. 4|oz. 



71 



72 

 73 

 74 

 75 

 78 

 77 

 76 

 79 

 80 

 81 

 82 

 83 

 84 

 85 

 86 

 87 

 88 

 89 

 90 

 91 

 02 

 93 

 94 

 95 



1-314 

 1-354 

 1-397 

 1*447 

 1-487 

 1-528 

 1-574 

 1-619 

 1-666 

 1-715 

 1-765 

 1-802 

 1-868 

 1-902 

 1-982 

 2031 

 2-087 

 2144 

 2-205 

 2-255 

 2-312 

 2-370 

 2-430 



