Gardner was employed to construct a drill; but his efforts failed of success after an expenditure of thirteen hundred dollars. A Mr. Butler was engaged to devise a machine, but in the course of studying the subject, his health failed and his services were lost.

A Mr. Hanson completed a machine which promised some success; but on trial it proved a failure.

A second machine called the Brooks, Burleigh and Gates drill, was made under the direction of the commissioners at Fitchburg. This machine was put upon the works and used for several months.

A third machine, called the Burleigh drill, an improvement upon the preceding one, was next produced, which is now at the works on the East Heading.

About $13,000 was spent upon these experiments, resulting in the construction of the Brooks, Burleigh and Gates drill, and the manufacture of four of them. About one-half of this expenditure may be charged to these last drills; the other was unproductive of anything of value.

The Brooks, Burleigh and Gates drill was patented, but the Commonwealth has the right to use them in the construction of the tunnel.

These machines will now be described.

THE HANSON MACHINE.

This machine has a cylinder and valve motion, similar to a steam-engine.

The piston is hollow, the drill-bar which may be of any required length, pa.s.sing through it, is moved with the piston, by means of four wedges or cams on each end of the piston; these cams are pressed on the drill-bar by means of sliding collars forced upon them by a complex arrangement operating alternately. The drill-bar is rotated by means of a ratchet operated by a spiral groove in the shield of the machine. The main difficulty in this machine was in the complex arrangement for forcing the collars upon the cams or wedges. It did not work well in a horizontal position. The machine consisted of one hundred and twenty pieces, and weighed five hundred and ninety-five pounds.

THE BROOKS, BURLEIGH AND GATES MACHINE.

This machine has a hollow piston, the drill-holder being a screw pa.s.sing through the piston, moving with it, and fed through it, by means of a nut on the end of the piston-rod. This nut is held by means of a cap or union nut, as it is called, the union nut being screwed on to the coupling, and the coupling nut screwed to the piston-rod. The feed-nut protrudes through the union nut, and is allowed to turn round in it. On the end of this feed-nut is a ratchet gear covered by a ratchet-band with an arm upon it, all moving with the piston. The ratchet arm moves up and down in a spiral groove, the groove being in a shield attached by screws to the cylinder; on the ratchet-band there is a pall and two springs, one under the other. One of the springs holds the pall in gear, the other holds it out of gear. As the piston moves down, the outer spring comes in contact with a trip which is on the shield and is lifted up, allowing the under spring to throw the pall into the ratchet, and as the piston is moved back, turns the nut round, thereby feeding the screw forward. At the extremity of its backward stroke, the pall comes in contact with another trip on the shield which lifts it out of gear, the outer spring having a catch upon it which holds the pall when thus lifted out. The rotary motion is given by a ratchet on the coupling-nut, covered by a ratchet-band the arm of which moves in a spiral groove in the shield similar to the other, only having a spring to hold the pall in the ratchet; this rotates all the parts on the piston except the ratchet-bands and cross-head. The latter is held between two check-nuts on the coupling-nut. To this cross-head is attached a bar which communicates with a valve which opens the port when the piston moves back, and shuts it when it moves forward; the air is always on during its backward stroke. The piston having a greater area on the forward than on the backward stroke, overcomes the backward pressure and moves the piston ahead, and when cut off, the continued pressure forces the piston back.

This machine is automatic; generally running until some portion of it is destroyed. No part of the machine has been found strong enough to withstand the friction upon it for any considerable portion of time. The union nut has proved its weakest point, and the breaking of this generally destroys that part of the piston to which it is attached.

Another point of weakness is the feed ratchet-band, the springs of which are almost continually breaking.

The machine consists of eighty pieces; twenty-three of which are screws, fifteen pins, and seven pieces of cast iron. It weighs 240 pounds, runs about 200 strokes per minute, and costs about $400. Its longest run without breaking has been five days. The run of one of them two days without breaking during the time, is considered fortunate. The average breaking is more than one a day. A table showing the list of breakages will follow this description.

The piston-head of this machine has a diameter of 4-5/8 inches. The diameter of the piston-rod is 4 inches at the large end and 2-1/4 at the small end.

So there are 12-87/100 square inches of air area to drive the drill ahead into the rock, and 4-23/100 to draw it out; but as the air is not taken off from the front end, the actual pressure is upon an area of the difference between the two, or 8-64/100 square inches.

Table showing Number of Drilling-Machines Broken, &c.

Column Headers A. No. Machines Broken.

B. Cross Heads C. Cylinder f.l.a.n.g.es.

D. Coupling Nuts.

E. Feed Springs.

F. Feed Palls.

G. Ratchet Covers.

H. Valve Stems.

I. New Packing.

J. Tapper Bars.

K. Screw Spindles.

L. Union Coupling Nuts.

M. Feed Nuts.

N. Shields.

O. Piston Heads.

====================================================================== 1866. [A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O]

---------------------------------------------------------------------- July 21, 32 5 2 4 3 2 2 1 10 7 - - - - - 31, 67 7 2 1 10 4 5 2 18 14 2 3 - - - Aug. 7, 75 4 1 - 18 15 8 4 39 6 4 - - - - 14, 76 6 - 5 25 17 11 3 - 10 1 6 1 1 - 21, 65 7 1 3 28 15 13 7 - 12 - 1 2 - - 31, 102 1 1 9 64 7 18 2 - 10 2 4 5 1 - Sept. 7, 65 1 1 - 27 4 24 - - 5 2 1 1 - - 14, 60 2 5 - 23 2 12 2 - 10 - 3 2 1 1 21, 56 1 1 1 28 6 13 - - 3 - 1 2 2 - 30, 56 3 2 1 31 3 16 2 - 4 - 1 9 1 - Oct. 7, 54 7 - - 39 2 7 1 - 9 3 - 1 2 - 14, 53 5 1 2 28 5 10 1 - 9 1 4 6 2 - 21, 58 3 - - 28 4 13 - - 9 3 - 4 2 - 31, 77 7 1 2 63 4 11 2 - 12 1 2 6 2 - Nov. 7, 38 2 - 2 19 3 13 - - 8 2 - 3 4 - 14, 40 1 1 - 17 2 9 - - 8 3 2 4 - - 21, 44 - 1 - 32 1 4 - - 7 - 1 1 1 - 31, 66 - - - 34 2 11 - 13 8 1 1 - 1 - -------------------------------------------------------------- 1,084 62 20 30 517 98 200 27 80 151 25 30 47 20 1 ======================================================================

About forty of the Brooks, Burleigh and Gates machines have been used at the tunnel; of these eight or ten were originally vertical, and intended for use at the Central Shaft. At the commencement of their use, the machines were new and had their best wear in them; there were from twenty to twenty-four at the beginning. In a short time they began to break down, but by putting on a large repair force and converting the vertical machines into horizontal ones, a fair supply was kept up for from two to three months, at the end of which time the greatest machine progress was attained, viz., fifty-four feet and six inches, in September. After that the progress diminished very much, and in proportion to the giving out of the machines. It is the opinion of the engineer that if a constant supply of machines could have been furnished, that the progress would have reached a point much beyond that obtained by hand labor; but with the stoppage of the supply, the number of machines that could be kept in working order was daily reduced, and at last it fell down to two or three, and finally, at times, none were in condition to work. The frames were, however, kept in the tunnel to await the completion of the Burleigh machine, the reception of which was r.e.t.a.r.ded till late in October; much beyond the time antic.i.p.ated by the commissioners, although the work of their construction was carried on continuously night and day. They came at intervals of several weeks, two at a time; the first of which were put into the tunnel on the thirty-first day of October. Through the month of December, four of these machines were at work.

THE BURLEIGH MACHINE.

Has a solid piston (so called,) which has a hole in its back end to allow the feed-screw to pa.s.s in without touching; the drill is secured to this piston. On the back end of the piston is a section of a ball used as a cam, which works the valve and the feed-motion. The valve is rotated by a rod lying on the band of the cylinder; upon this rod are two cams which perforate the band of the cylinder. The action of the piston brings the ball on its end in contact with these cams, rocking them up and down; the rod to which they are secured being connected with the valve, imparts to that its motion. This machine is fed altogether on ways, or a bed-piece, upon which is the feed-screw; the feed-nut is upon the end of the cylinder-band. To this feed-nut is attached a feed-ratchet, which is held between two collars, allowing it to turn round. Upon the cylinder-band is a lever, one end of which pa.s.ses through the band; upon the other end is a pall. The motion of the piston raises the lever up, pressing the end containing the pall against the ratchet which turns the nut on the feed-screw, thus moving the machine forward. The rotating ratchet is in the band of the cylinder and has a spline in it, and a pall on its outside. The piston having a spiral groove is turned by this ratchet as it moves down. On the return of the piston, the pall drops into the ratchet and then the piston is turned.

The piston is not enc.u.mbered with any machinery, and moves alone; its area of air is greater on the forward than on the backward stroke; the alternation of the valve admits the air. The machine, like the one last described, contains eighty pieces; it has the same number of screws and pins, and weighs 372 pounds including the ways or bed-piece; without the ways its weight is 212 pounds. Its number of strokes is about 300 per minute, and its blow somewhat lighter than that of the other. This machine is not entirely automatic; the feed-motion not working regular; when it does not, it is fed by hand, which is a simple process.

These machines stand the work much better than those first made at Fitchburg. Their average time in the tunnel without repairs in the interval, is about five days; they have needed repairs in two days; one remained at work fourteen days. They accomplish double the work without repairs that those do which were made after the previous pattern. There is a further advantage in using the Burleigh machines; their breaking, when it occurs, is not very serious, the injured parts consisting mainly of cams, can generally be replaced at the tunnel; whereas for the repairs on the Brooks, Burleigh and Gates machine, the dependence to a very great extent has been upon the machine shop at Fitchburg.

The piston-head of this machine has a diameter of 4-25/100 inches. The diameter of the piston-rod is at the large end, 3 inches, at the small end, 2-75/100 inches.

So the number of inches of air area, is 8-20/800 when the drill is propelled upon the rock, and 7-7/100 when returning from it.

A full complement of men to work the machines first used, would be, perhaps, thirteen. Mr. Gates, who superintended their operation in the first instance, began with fourteen, but they were reduced to thirteen.

The Burleigh machine practically requires feeding, and a full set at work would probably demand fifteen men for their successful operation.

The value of these machines has not yet been ascertained. The Committee are of opinion that when a full complement shall have been obtained, so that the workmen can have at all times a full supply upon the frames, that greater progress can be obtained by them than by hand drilling; and after a few months operation, the cost of using them, in comparison with hand labor, can be fairly tested. But as the Brooks, Burleigh and Gates machine has been abandoned, no useful results would be obtained by comparing the expenses within the tunnel during the months of July, August and September, with three corresponding months when hand drilling was carried on, and no satisfactory comparison can be made between the working of the Burleigh machine and hand drilling, until a sufficient number of machines has been introduced into the tunnel to keep the men fully employed. It is to be hoped that machines sufficient to make the test may be soon obtained, and that this desirable information may be made known.

The introduction of the first machine into the tunnel, before its capacity, strength, and expense of working had been fully tested, was unfortunate, inasmuch as its use there delayed the progress of the work.

The second machine gives such promise of success, that it will be continued in use in the tunnel until a fair test has been made. But should the Burleigh machine prove unsuccessful, and further attempts with machines be attempted, the Committee recommend that their usefulness be tested outside of the tunnel, and meanwhile the excavation with hand drills be resumed.

EXPERIMENTS WITH DR. EHRHARDT'S POWDER.

The first blast was fired in the tunnel at the East End on the 20th of November, but owing to the presence of charcoal or some other substance in the article, a poisonous gas was evolved which effected the miners disagreeably, and drove them from the work. The subsequent experiments at this point were not satisfactory, and were discontinued, and subsequently resumed at the Central Shaft, where it was used most of the time for a week, varying its composition from time to time. At the close of the week, while preparing for the last blast, a premature explosion took place, resulting in the death of one of the miners, and the injury of three or four others.

The material result of this experiment was as follows:--With 261 days'

work and 139-1/2 lbs. of powder, 202 buckets of stone were removed; while in the preceding week, using common powder (schaghtic.o.ke) with 251-3/4 days' labor and 236 lbs. of powder, 168 buckets of stone were taken out. The cost of the experimental powder is about twice as expensive as the common powder, and its superior strength is apparent from the above result.

EXPERIMENTS WITH NITRO-GLYCERINE.

During the summer, some experiments have been made with this explosive agent. A quant.i.ty, costing $934.29, was brought to the works by Colonel Schaffner, who exhibited the action of the material in various ways, with a view of testing its power, and the comparative safety of introducing it instead of powder. After repeated trials outside of the works, during which about three-fifths of the material was consumed, it was introduced into the tunnel at the West Shaft with the following result: It was used for three days at the East heading of the West Shaft; the advance made in the heading was for the time, 14-1/2 feet;--being an advance of 4.82 feet per day, and at the rate of 125.33 feet per month.

In these three days there were taken out of the enlargement 151.76 yards of stone. To remove this quant.i.ty with powder would cost, on an average, per yard, $9 84 Actual cost with glycerine, 6 20 ----- Difference, $3 64

Multiplied by 151.76, gives. $552 40 In the same time there was removed of heading 60.15 yards.

To remove an equal amount by powder costs, per yard, $16 25 Actual cost with glycerine, per yard, 6 05 ------ Difference, $10 20 $10.20 multiplied by 60.15, gives 613 53 -------- $1,165 93 Cost of the glycerine used during the three days, being 2/5 of $934.29, 350 36 -------- Saved, by using glycerine, in three days, $815 57

Which is a saving by the use of glycerine, per day, of $276 85.4 and allowing three hundred successful working days in the year, an annual saving of $81,557 40

The progress made at the West Shaft on the East heading the present year, ending December 31, 1866, is 626 feet and 8 inches. This progress was somewhat lessened by the influx of water in December. The monthly advance has been 52 feet and 2 inches. The average of the eleven months ending with November is 53 feet and 6 inches. a.s.suming the progress made with glycerine during the three days of its use to be obtainable throughout the year, the monthly progress, using that material, would be 120 feet and 10 inches, on a calculation of twenty-five days to a month, which would give an annual advance of 1,450 feet.

Without vouching for results so favorable to the progress of the work, it is impossible to overlook the importance of the experiment; and the Committee are of opinion that this material, if it can be procured, should be introduced into the tunnel and shafts, and a thorough experiment made, in order to determine whether it can be used with an advantage even approximating to that shown by the first trial.