Part 3 (1/2)
_Larger Holes in Glass_--The hly satisfactory for anything but shth of an inch or more, is needed it is better to use a copper or brass tube This tube may be held in an American hand-drill, but a mixture of carborundu end Tube or drill must be lifted at frequent intervals in order to allow a fresh supply of the grinding uide is quite essential in the early stages of drilling; otherwise the end of the tube will stray The speed of cuttinga number of radial slots in the end of the tube; these serve to hold a supply of the grindingLenses_--This is scarcely within the scope of a book on glass-blowing for laboratory purposes, but it round byis done with coarse carborundues are carried on with finer and fineris by the use of jewellers' rouge on theGlass_--If a new file, thoroughly lubricated with a solution of camphor in oil of turpentine, is used, there is but little difficulty in filing the softer glasses A slow movement of the file, without excessive pressure but without allowing the file to slip, is desirable
After a ties of the file teeth ear down and it will be necessary to replace the file by another
_Grinding Stoppers_--This is, perhaps, thethat the laboratory worker will need to perform, and for that reason, rather full details of the procedure are desirable
A very crude for out the neck and the lass which is intended to for the surfaces with athe stopper in by hand
Frequent lifting of the stopper is necessary during grinding, in order to allow fresh supplies of abrasive material to reach the contacts When an approximate fit is obtained, the coarse abrasive should be washed off, care being taken that the washi+ng is complete, and a finer abrasive substituted After a while, this is replaced in its turn by a still finer grinding ive a satisfactory stoppering if the angles of the plug and socket correspond very closely before grinding is coles, then no aood result
The reason for this is that the plug will beco as to assuhly truncated cone; the socket will assu plug and socket
Satisfactory grinding may be carried out by the use of copper or type- Such cones should be mounted on a mandrel which will fit into the chuck of the American hand-drill and turned on the lathe to the desirable angle for stoppering A number of these cones will be necessary A number of similar moulds, that is to say blocks of type- in size and angle to the plug desired, should be made also These must be rotated, either in the lathe or by otherIf but few plugs are to be ground it is unnecessary to provide around into the mould in a
[Illustration: Fig 14]
When the socket and plug have been ground, by the successive use of cones and le, so that they correspond al into the socket by grinding-in with a fine abrasive, in the h it would bewith the for of stopcocks into two parts; shaping by heat and grinding, ill consider the whole operation here, and take for our exa 14
The ”blank,” _f_, that is the socket before grinding, isinto the form shown by _a_
Two zones on this tube are then heated by means of a s its axis, thus producing two raised rings as shown by _b_ Two zones, slightly towards the outer sides of these two raised rings are heated and the tube is drahile air pressure is maintained within This produces two thin-walled bulbs or extensions similar to those shown by _c_ One of these extensions is now broken off by e of a file or other piece of lass are rounded in the flame The other extension is left to serve as a handle We have now a piece of glass like that shown by _d_ Now heat a spot on the side of this, lass is on the point of beco the intensely heated end of a smaller tube in contact with the heated spot Without disturbing the relative positions of the two tubes, press the smaller tube down on a thin steel wire, so that the wire passes along the tube and enters the soft glass; thus for a projection inside the sockets as shown by _e_ The wire ain immediately When the wire has been withdrawn, heat the place where it entered to dull redness, in order to relieve any strain; break off the thin extension, which up to the present has served as a handle, round off the broken edges in the fla to the opposite side of the socket; the socket at this stage being shown by _f_ The ”blank” for the socket is now completed, but it must be heated to dull redness in order to relieve strain and be placed in an annealing oven, where it should be annealed for so offers no special difficulty; it isit axially until a14, is produced; the end of this is heated intensely and brought in contact with the rather less heated side of a glass tube which has been drawn to the shape desired for the handle; when contact is lass tube, thus producing a hollow join The ends of the tube are sealed and the botto the finished ”blank” as shown by _h_ This blank is now held in a pair of asbestos-covered tongs, heated to dull redness all over, and transferred to the annealing oven
When cold, the socket is ground out by the secondStoppers”; that is to say, by round to fit in a corresponding mould When the fit is al, and the final finishi+ng is made with fine abrasive powder Great carethat there is no accumulation of abrasive ; if this is allowed to occur there will be a ring ground out of the socket where the holes htness of the finished stopcock will be lost
_Marking Glass_--As a preli and calibrating glass apparatus, it is convenient to consider the variousthese are, the writing dia-wheel, and etching by means of hydrofluoric acid Each produces a different class ofand each is worthy of independent consideration
_The Writing Diament of ”bort” which is usually mounted in a thin brass rod Such a diamond, if properly selected, has none of the characteristics of a cutting dia diamonds” which will produce a definite cut These should be rejected
The writing diamond is used in much the same way as a pencil, but is held more perpendicularly to the object, and a certain amount of pressure is necessary The h fairly definite, lacks breadth, and this is a disadvantage where the ea number of parallel scratches
_The Abrasive Pencil_--A rod of carborunduround or filed to a point, and this for produced is rather less definite than that produced by a writing dia broader
_The Cutting Wheel_--”Cutting” in this case is scarcely the ideal expression, it should rather be ”grinding,” but ”cutting” is raduations e of a small, thin, abrasive wheel which is mounted on the end of a small mandrel and driven by a flexible shaft from an electric motor or any other convenient source of power The depth of the ht pressure will suffice
_Etching_--This is often the quickest and easiest way of lass apparatus The object to be hly with a thin filh the paraffin wax by means of a needle point, and the object is then exposed to the action of hydrofluoric acid If a shallow but clearly visibleis desired, it is well to use the vapour of the acid; this h on which the object can rest with the marked surface doards A little of the commercial hydrofluoric acid, or a mixture of a fluoride and sulphuric acid, is distributed over the bottoement is allowed to stand for about an hour The object is washed thoroughly and the paraffin wax re off or by the use of a solvent, and theis desired, in order that it ment, a better result is obtained by the use of liquid coen fluoride in water The acid is s have been made on the paraffin wax film, and allowed to reeous to repeat the