A PURCN FOR STRAIGHT RUBBER TEST PIECES, Hy H A R R Y 1,. >I,LLS.
ReccivedJan. 5 , 1912.
Although the ring iorm oC test piece has recently hecome popular, many workers still preier the straight test piece, as the usc of the latter does not involve certain serious errors to which the ring piece is subject. I . I h c devices for preparing ring test picccs have been perfected beyond those for handling straight pieccs, and the ring picccs arc therefore easier to manipulatc; b u t by thc use oi the punch herein described the strip pieces can be prepared with even less trouble than the rings. All thosc who have tried punchinr: test pieces te the difficulty in preparing unifomm pieces of a regular cross section t h a t can be easily measured. The softer the stock the more it yields under thc knife or punch, and the more likely will the section depart irom the dcsired shape. Our work deals largely with pure gum stocks, and the method described has becn iound to work quite satisfactorily. Scveral workers have attempted to mould the strips into the dcsired form, but it is difficult to obtain uniiormity throughout the narrow portion. It is essential t h a t the section should be uniform anti easily measured; ~ J S O t h a t the edges should be clean, as i s , tear vrill rcadily follo\v a slight chock. I t has been found much more satisfactory to punch away the sides uf a Aat strip, leaving the test portion between two stout ends, as in Pig. 2 . The strip is moulded to the form shown in Fig. I ,
- ~ -
7
.-
is lifted out, the punched piece still adheres t o it. Without removing this piece the strip is replaced in the nest, this time with the cut edge forward. Care is taken to have the same surface u p in both cases, as the parallelism of the width of the test pieces is thereby assured. The second side is punched out, the strip taken out of the nest and the punched pieces
t
.. 1.
753
e
.rig,-
torn or cut free. Two marks a t a unit distance are then placed on t h e strip and after measuring is ready for testing. Thr strips arc uniiorm to within a few thousandths of a n inch, a,nd the cross section is almost a rectangle, which permits of accurate measurement by platen calipers. l'he knives arc removable, and test pieces of various lenxths and widths may be cut from strips of any thiclincss.
~Jq--Ir'''''-i l... -.
--2-
--,*'+a
-FifZ--
in bolted moulds, each rnonld producing eight strips. The punch (Fig. 3) is equipped with a sharp, thin, curved knife, set firmly in the vertical slide. A stop prevents it from touching the cast iron bed plate. A "nest" into which the strip fits snugly prevents the rubber from spreading while being cut. The nest is secured t o the bed plate by thumb screvs, and it can be adjusted to regulate the thickness of the strip. To operate, a few thicknesses oi manilla paper are laid in the nest: the knife cuts into these, but does not reach t h e be.d plate. The strip is then placed in the ncst and one side punched out by operating t h e pedal. The knife is so shaped that a little of the ruhbcr a t each end is lcft uncut; thus, r h e n the strip
nzisrrixcii i,~nuoa.~roil~. C O N I I \ - R S ~ . ~ ~ - J I E X I CR * N~ s i m xCOXPAUY, l'ouafox, C".,,,.. Mnic".
A LABORATORY GENERATOR FOR NYDROCHLORIC ACID GAS. 13s Eowm DOWZARD.
Rerfivcd Janiiniv 4. 1912.
In laboratories whcre dry hydrochloric acid gas is frequcntly or occasionally requircd, the apparatus illustratcd in the sketch will prove of value. On rcierrin,q to sketch, the apparatus will be seen to consist of a storage bottle fur comniercial hydrochloric acid, a flask to be half filled with concentrated s u l p h u r i c acid, and a bottle cijntaining concentrated
