[Reported expressly for the Scientific American.] On Wednesday evening, Nov. 28th., the usual weekly meeting of this association, under the new constitution, was held at its room, No. 24 Cooper Institute, this city Henry E. Roeder, chairman pro tern. ; Benj. Garvey, Secretary. The regular subject " Ashcroft's Low Water Detector "was here taken up. DISCUSSION. Mr. KochDuring the discussion upon the utility of this instrument on last meeting night, it was asserted that, although sediment or corrosion had collected upun the plug of the one in use at the Cooper Union, it would still melt, and that at the proper time. Since then we have had another opportunity of inspecting this ping, and now beg leave to submit it to the members present. It will be observed that a portion of the plug is full of sediment. Now, the question arises whether this feature will hinder the action of the plug as intended. Mr. GrayThe representative of Mr. Ashcroft has said he would give a large sum to any one who could procure a plug that would not fuse, after many months use, and that the one now before us would certainly melt. The surface of it is coated to such an extent that, to me, it seems very doubtful. I should like this point settled. Mr. KochI would request that the plug be passed around among the members, that each may decide in his own mind whether the portion thus coated will fuse. (Here the plug taken from the instrument in use at the Cooper Union was passed among the members by the Secretary. A thick coating of sediment or mud had settled in the branch tube and upon the bottom of the plug.) Mr. MerriamThe mud being deposited in the branch tube certainly presents a serious fault. The sediment being a poor conductor, it would prevent the plug from tusing at the proper time. I have ascertained, since our late discussion, that the instrument that gave an alarm at the Astor House with the cocks of solid water, could not have whistled, but merely made a hissing noise, easily distinguished from an alarm when made by steam. Mr. GarveyThe fact was stated it blew, not hissed ; that there was sufficient generated steam within the tube to keep the whistle blowing. Mr. StetsonIt seems hardly fair to judge of the value of the instrument because of the deposit of mud upon this plug. If the sediment prevents the transmission of heat, the metal surrounding it will radiate sufficient to melt the plug. Mr. GrayHow long a time would that require ? Some boilers are so peculiarly constructed that, in the time necessary for the transmission of the heat by radiation, great damage might ba done, and perhaps lives lost. Mr. MerriamIron is not such an excellent radiator of heat that it would raise it fro such a point necessary to fuse the plug. This feature could never be depended upon. Mr. PittHow long has this plug been in use? Mr. GrayBut a little while ; some five or six times ; and the plug was detached from the instrument this evening about eight o'clock. Mr. KochMr. Ashcroft is not in town ; but his representative (Mr. Hart) was requested, upon last meeting night, to be here this evening, and it is curious, to say the least, that he is absent. Mr. MerriamMr. Hart waited upon me last week and signified his intention of being here this evening. Ha also wrote Mr. Ashcroft, in relation to the proceedings of this society, in reference to his detector. Mr. GrayTwo months ago, in examining the plug now before the society, I discovered a number of little specks upon it. Yet I am much surprised to see it so nicely coated at this period. I thought it would require years to cover it in such a manner. An argument then ensued upon the compressed air within the ball, and as to whether, if the warm water at the bottom would not replace the cold at the top, a still thinner fluid, such as steam, would replace it ; and did not the tubs of the detector partake of the nature of a barometer. The following is the gist of these remarks: Mr. GrayHow does cold water find its way to the ball at the top of the instrument ? Mr. KochAs soon as steam forces the water np to the globe, the inventor contends that it remains there that there is no circulation of it, and thus, with the tube and ball being exposed, the water becomes cold. At the trials at the Cooper Union, the time that elapsed between letting the water down to the alarm point, and when the whistle blew, when the tube was full of compressed air, was sufficient to blow up the boiler fifty times ; but upon the second attempt, when that air was absorbed, the detector started and worked very nicely. Mr. BabcockWater will circulate when in such a condition. I have witnessed experiments which have demonstrated this fact- A pipe some three or four feet in hight, with an internal diameter of three-quarters of an inch, connected with a boiler by a horizontal branch piece six inches in length, having a glass top, showed that water and steam would rapidly change their positions, and vice versa. At this period, Mr. Hart entered the room. Mr. StetsonOne question arisesit is this: What means are adopted to insure the rapid and certain exchange of steam for water when the water falls below the alarm point ? Mr. HartThe way we know that it does is by experience and practical illustration. Mr. PittHow does the gentleman account for the large collection of sediment upon the plug just handed him ? Mr. HartI have understood that the boiler is only occasionally used, and the only reason to which I can attribute it is because of the non-working of the boiler. This would give an opportunity for the prasence of a large volume of air in the tube------ Mr. Koch (interrupting)Is that a deposit of air upon the plug ? (Laughter.) Mr. HartNo, sir. I should call it rust. I have never seen one like it before. Mr. KochThis discussion seems to me to be a very curious one. Mr. Hart attributes this deposit to the non-working of the boiler. Now, sir, this deposit is actually rust, and the more the boiler is used the greater will be the deposit. Mr. Hart here arose to explain that, having but little experience with the instrument, he was not capacitated to answer all the questions the members asked ; that he came there only to explain the operation of the detector, as well as able, during the absence of Mr. Ashcroft, who was in Boston, in attendance upon a sick member of his family. Mr. KochTo me, there seem to be two points to consider, viz.: Will the air in the globe really be absorbed by contact with the water, and will the plug be hindered from fusing by the coating it has received ? If the air within the tube is not absorbed, it will act as a cushion to the water, and its falling will be so tardy, it will always be a matter of great danger. If the deposit upon the one end of the plug will not hinder the balance of it from fusing, this question may be answered favor ably ; but if this deposit is corrosion, it will utterly fail to answer the purpose intended. At this juncture, much discussion arose in relation to the disposition of the subject. The society had taken up two entire evenings in reference to the utility of the detector, but because of the divers opinions of its members, had failed to reach a point where a vote could be taken upon the committee's report. The committee asked to be discharged from the further consideration of this particular question, which was granted. It was decided that anew committee should be appointed, upon whom would devolve the duty of obtaining new facts, new opinions, &c, and to test, by further experiments, its utility for the work intended. To this end, the representative of Messrs. Ashcroft & Co. promised to supply an instrument simplified in its many parts, to allow the committee, by additional experiments, to determine upon the points in issue ; further, he promised to do everything in his power to facilitate the investigations. After several ineffectual attempts to obtain a new committee from the members present, the chairman postponed the entire matter to the subsequent meeting. There was, seemingly, an evident dislike, on the part of the members, to serve upon this committee. The reason of such disinclination was not apparent, except that the respective business of the gentlemen precluded the possibility of their devoting as much time to it as the importance of the case demanded. The subjects for consideration at the next meeting will be "Warren and Bank's Low Water Detector," and " Shrimpton's High Pressure Condenser." On motion, the association adjourned.