HARDWICKE'S SCIENCE-GOSSIP. 



17 ^ 



Fig. 19. Punches for 



making microscopical 



cells. 



respect to each other. In the auuexed diagram the 

 three outer circles correspond with gun punches of 

 the respective numbers indicated, but the two inner 

 ones are shoemakers' punches 

 of a commoner description, 

 although answering the pur- 

 pose sufEciently well. The 

 next step should be to obtain 

 a series of brass cones of the 

 form represented at A, B, fig. 

 19, one fitting into each of the 

 punches except the smallest, 

 while the projecting portion 

 B should fit very accurately, 

 and not too tightly, into the 

 opening made by the punch 

 next smaller in size. Then 

 commencing by punching out 

 the smallest disc, the smallest 

 guide-cone is next inserted 

 and carefully fixed in itsplace, 

 turning the card over so as 

 to use the sharp edge of the 

 aperture ; the puncii is lastly 

 placed over this, which guides it to its place, 

 when a sharp blow cuts out the portion re- 

 quired. The different sized rings being thus cut 

 in succession leads to the least possible degree of 

 waste in the material as well as saving in time. 

 In the diagram the front of the outer punch C has 

 been cut away to show the position of the cone 

 in its interior and to give a clearer view of the 

 arrangement and its action, DD showing the -width 

 or the resulting ring, which cau be varied only by 

 the relative proportions of the punches, which must 

 he determined at the outset. 



The next stage in the process will be to saturate 

 them with varnish. Let a thin solution of shellac 

 be made in rectified spirit of wine (or if cost be 

 more a considerationthan ha.gr&\iGe,met//?/lafed spirit 

 may be used), and placing the rings in a wide- 

 mouth phial, let them be covered with the solution 

 and left so for two or three days closely corked up, 

 when they will be ready to be pressed and dried. 

 Having provided a few score pieces of common 

 window glass about one inch square, let these be 

 spread out on the table and the rings taken out one 

 by one, placed upon them, one in the centre of each 

 square, and then placing them one upon another 

 with a spare piece of glass on the top, in a pile just 

 sufficient to be taken up in the grip of a wooden 

 American clothes-peg, which will thus act as a vice 

 and squeeze them flat, and in which position they 

 may be left until quite dry. I have a stout wooden 

 box about one inch deep and five or six inches wide, 

 partitioned off into compartments, a little over an 

 inch wide, and these being filled with the glass 

 squares containing the rings, a common wood screw 

 is passed through the side opposite the centre of 



the squares, which then screws the whole up into 

 a compact mass with any amount of pressure. Of 

 course any description of sized or unsized paper, 

 parchment-paper, leather, or any other soft sub- 

 stance, may be cut in the same way, and will serve 

 equally well when only dry objects are to be 

 mounted in them ; but when required for fluids, 

 pure tin will be found one of the best materials for 

 the purpose, especially as it can be cut in the same 

 manner and with the same punches. This metal 

 may be obtained of Stanton Brothers, in Shoe-lane, 

 rolled to any thickness, at about half a crown per 

 pound, half price being allowed for the spare clip- 

 pings in exchange, so that but little loss will be in- 

 curred by waste. As this material, however, can 

 hardly be cut conveniently of a thicker substance 

 than about the thickness of a new shilling, glass has 

 been resorted to in all such cases as require a 

 deeper cell for the retention of fluids. To " punch " 

 a hole through a piece of window-glass may seem 

 a very unlikely proceeding, yet it is in reality one 

 of very easy accomplishment. If the glass be se- 

 curely cemented down with shellac upon a piece of 

 brass not 'less than an eighth of an inch in tliick- 

 ness and having a hole in it of the size intended, 

 the centre may be chipped out with a pointed 

 hammer, in a very few seconds, and a rough file will 

 then trim it to the edge of the brass, when it may 

 be removed, and after soaking in liquor potassse for 

 a few hours to remove the lac, may be ground true, if 

 greater perfection be desired. Erom the thinnest 

 covering glass and plates a quarter of an inch thick, 

 cells may be readily made in this manner. 



The last point to be attended to is securing the 

 ring firmly to the glass slip. If required for fluid, 

 nothing answers so well as marine glue, taking care 

 that all parts be sufficiently heated and well pressed 

 together ; but if only needed as drt/ cells, a far less 

 troublesome process will suffice. Eor the circular 

 tin and paper cells I have found no preparation so 

 effective, or so little trouble, as " Priest's Diamond 

 Cement." The parts to be put together should 

 be warm and free from grease, and when metal is 

 being fixed, the whole should be warmed up after- 

 wards, to about the melting-point of the cement, 

 as this keeps secure the attachment of the 

 latter. Eor putting on covers it has too the merit of 

 not "running in" while it holds the glass most 

 effectually and is almost colourless. A thin coating 

 of this upon all insecurely fixed cells, embracing the 

 side and touching the cover at the top and the 

 glass slip beneath, renders the whole perfectly se- 

 cure by tying together, as it were, the cover and the 

 slip, with the ring inside as a support. This cement 

 may be purchased at any chemist's, price one shilling 

 per bottle, holding about three quarters of an ounce, 

 and is prepared for use by placing the phial for a 

 few minutes in hot water. 

 St. Giles-street, Norwich. W. K. Bridgman. 



