410 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[December, 



3 ft. S in., its net capacity about 520 gallons ; and the space occupied 

 by two individuals would reduce the contents to about 49it gallons of 

 air. To avoid any complication in the experiment by the intro- 

 duction of more air than the actual contents of the bell, and the neces- 

 sity of taking down cylinders with compressed air, to prevent the 

 water rising in the bell, it was lowered so that the whole of the bell 

 was immersed 9 inches below the surface of the water, sufficiently to 

 etfectuallv exclude all external air without compressing the air within 

 too much. The experiment commenced at three o'clock, and was 

 continued until half past four. In this time no inconvenience was ex- 

 perienced from the deterioration of the air in the bell, and in their 

 opinion they might have remained at least half an hour longer, but 

 the approaching darkness induced them to give the signal to be drawn 

 up; having fully verified the experiment at the Polytechnic Institution 

 by remaining, without a fresh supply of air, for an hour and a half. 

 If Dr. Payerne has any doubt as to the correctness of the experiment, 

 the Editor will be mo'st happy to accompany the Doctor, and repeat 

 it with him, or any other person he may nominate. 



In the first of these experiments the quantity of air in the bell would 

 allow scarcely two gallons, in the latter rather more than two gallons 

 and a half per minute for each individual; yet those limited quan- 

 tities proved sufficient, without producing any disagreeable sensations 



" Facts are stubborn things," Doctor, and in this instance they will, 

 we expect, prove too obstinate to yield to any mystification, though 

 backed by the authority of the French Institute. No one would 

 descend in a diving bell for fresh air, however supplied, nor select 

 such a residence as a restorative of health ; existence in a diving bell, 



must, after all, be a matter of endurance, and the facts we have stated 

 show the absurdity of applying vague opinions respecting the quan- 

 tity of aiv requisite for healthy respiration, as data for calculations 

 of the quantity of air necessary to support life. 



We infer from Dr. Payerne's letter, and from circumstances which 

 have since come to our knowledge, that he now disclaims all pre- 

 tension to generate oxygen gas, and that he claims only the plan of 

 absorbing the carbonic acid gas resulting from respiration by the use 

 of quick lime and potash. If this be the case, on what foundation 

 does he rest his assertion, that he could " remain in the diving bell 

 an indefinite period of time t" Though Dr. Payerne may, now that 

 his experiments have been submitted to scrutiny, disclaim tlie power 

 of generating " good air," there is little doubt he in the first instance 

 wished to convey such an impression ; else, by what conformity of 

 blundering could all the reporters have agreed in so representing 

 Dr. Payerne's powers. If he did not originally profess to be able to 

 generate oxygen gas, what becomes of the declaration in the semi- 

 official report, that "General Pasley had no doubt of the goodness of 

 the Doctor's air?" and how can he defend the first proposal to descend 

 without any cylinders of compressed air to keep out the water ? 



We hope vve have satisfied Dr. Payerne, or at least the public, that 

 his experiments in the diving bell at the Polytechnic Institution, sig- 

 nally failed to prove that he possesses any peculiar and valuable 

 means of purifying or of generating air ; and that his calculations of 

 the quantities required for the support of life are extravagantly erro- 

 neous. We will not deny that he has done some good by the an- 

 nouncement of his discoveries; it has attracted attention to the sub- 

 ject, and thereby elicited useful and curious facts.] 



SUGAR MAKING APPARATUS. 



Sir — The importance of any improvement in the process of" Sugar 

 making," in the colonies, with respect either to economy in the manu- 

 facture, or the quality of the product, I trust is a sufficient apology 

 for calling the attention of your readers to a description of an appa- 

 ratus employed by Mr. Alfred Stillman, an engineer of this city, who 

 has for a number of years been engaged almost exclusively in the 

 introducing and perfecting of steam' machinery in the West Indian 

 islands. 



>> This gentleman, having occasion to put in operation a " Steam mill," 

 in St. Croix, conceived the project of converting to the purpose of 

 generating steam for the engine, that vast proportion of the heat 

 from the " megass fire " which is wasted beyond the " coppers." In 

 order to effect this, he placed the steam boilers directly behind the 

 " trains," in such a manner as most effectively to apply the waste heat 

 from under the " coppers." In this he so far succeeded as to require 

 no other fuel for generating steam, than sufficient to "put the mill 

 about" in the commencement of each day's work. 



His attention was next turned to the employment of the " exhaust 

 steam" for clarifying the "liquor." To do this, he employed tanks 

 of sheet iron, with double bottoms and traversed by a tier of copper 

 pipes, into which was introduced the escape steam from the engine. 

 The process of claiifying was in this way effectually carried on; and 

 by closing the escape pipe with a loaded valve so as to maintain a 

 slight pressure within, the effect was so much increased, that by 

 means of two or more sets of these tanks, the one discharging into 

 the next, a part or the whole of the process of concentration might 

 be thus performed, ami thereby dispense with a part or the whole of 

 the train of eoppers, rendering the megass fire more effective under 

 the steam boilers. 



Now, it is a point pretty well established iti practice, that in the 



evaporation of saccharine juices, the less the temperature of the 

 heating surface, the less of oxidation takes place in the saccharine 

 matter, and the more perfect the crystallization ; consequently yielding 

 a greater proportion of sugar and of better quality. 



Admitting this, it will be perceived that if, instead of the intense 

 heat of the megass fire and the limited heating surface, we employ 

 the temperature of skam with an unUmittd extent of heating surface, 

 a decided advantage is gained in these important particulars — the 

 quantity and quality of the product. 



The simple sketch accompanying this, will scarcely need further 

 explanation ; being merely a section of a reduced train of coppers, 

 A, A, A, with its flue, B, passing from the furnace, C, under and 

 through the two steam boilers. D, D, also two clarifiers, E, F, re- 

 presented, showing their construction and the manner of admitting 

 the steam. . 



The whole arrangement and operation is extremely simple, ana 

 very readily encompassed by such talent as is to be found on every 

 "sugar estate;" which has been satisfactorily demonstrated during 

 the last two years in St. Croix, and also during the past season on the 

 estate of Don Gasper Hernandez, Cuba, West Indies. 



Keiv York, July 1842. 



F. W. S. 



[Although portions (if not the whole) of the apparatus above de- 

 scribed are not new, we have thought proper to give our Transatlantic 

 correspondent's communication an insertion, as it shows what economy 

 there is exercised in the distribution of heat in the process of sugar 

 making. We may at some future opportunity, publish the process ot 

 sugar making in vacuo. — Editor.] 



