L. MECHANICS AND ENGINEERING. SI*? 



The conclusions to which they came are that the tunnel is 

 not a necessity for drainage, but that, in some cases, it proip- 

 ises increased economy in working mines, and in rendering- 

 available the now worthless ores in the Comstock lode, thus 

 becoming of national importance. The feasibility of the tun- 

 nel, the commission think, is placed beyond a doubt, its cost 

 being estimated at four and a half millions in gold, the work 

 to be done in three and a half years; and this period may be 

 considerably reduced if proper machinery be employed. 



Tli^ value of the bullion heretofore extracted from the 

 mines of the Comstock lode is estimated at $125,000,000, 

 wliile the present annual yield is about 815,000,000. The 

 commission believe that the lode is a true fissure vein ; but 

 whether it will continue to be ore-bearing can not be pre- 

 dicted with certainty. In deep mining the commission re- 

 gard the experiment of the tunnel as of great importance. 

 Report of the Chief of Engineers^ U. S. A., for 1871-2, 1127. 



WATEPv-PEOOF COxVTIXG FOR WALLS. 



The following coating has proved very effective in prevent- 

 ing the penetration of moisture on the weather side of walls : 

 Pitch, 50 lbs. ; rosin, 30 lbs. ; red ochre, 6 lbs. ; fine brick- 

 dust, 12 lbs. ; all boiled together, with constant stirring, and 

 then sufficient oil of turpentine about one quarter the vol- 

 ume of the above added to cause it to spread readily. It 

 is to be laid on as thin as possible with a bristle brush. 12 

 (7, &eptemhei\ 1872, 72. 



TREATMEXT OF NEW DWELLING-ROOMS. 



The dampness of newly finished rooms is not due so much 

 to the water used in mixing the plaster, as to the water of 

 hydration of the lime liberated by the action of carbonic 

 acid. The action of the small quantity present in the nor- 

 mal atmosphere would, however, be so slow, and the water be 

 liberated so gradually, that no injurious effects could result. 

 But as soon as the rooms become tenanted, the large amount 

 of carbonic acid given off in respiration causes such rapid 

 displacement of water, and with it other matters indicated 

 by the peculiar odor, that unpleasant and injurious results 

 may follow. Treatment of the rooms with carbonic acid, 

 before occupying them, suggests itself at once as a means 



