31
METHYL VIOLET TEST PAPER.
T h e composition of pyrophosphate of zinc is as follows : 2 Zn 130 42.763 per cent. 2 P 62 20.396 " 112 36.842 6' 7 0
---
-
-_-
%n P, 0,
304
100.000
,
0 r,
2 ZnO
p, 0 , Zn,P,O,
IC2 142 304
53.29 per cent. 46.71 ('
--__
6'
100.00
Nickel and cobalt form phosphates which behave precisely like the corresponding zinc salt ; both, however, are strongly colored, and SO can readily be distinguished from phosphate of zinc.
VIII. METHYL VIOLET TEST PAPER. Bs T.O'CONNOR SLOANE A. M., Ph. D. Seveyal years have passedsince it was first proposed to use methyl violet as an indicator or test for mineral acids in the presence of organic acids, Since it has also been used as a coloring matter for test paper it occurred to me that a few notes on the preparation and use of the paper would be of interest. I tried solutions of methyl violet of different strength iri dyeing paper. A solution of one part of violet i n four thousand parts of mater wa9 found to be sufliciently strong. A solution of double this strength gave a very goou color. Using paper dyed with the first solution I performed tlie following experiments: One cc. of concentrated hydrochloric acid was mixed with him one hundred cc. of water. The acid was of sp. gr. 1.197 corresponding to about 40 per cent. acid; the solution therefore was of four one thousands strength or four-tenths of one per cent. A piece of paper dipped in this solution did not show the rcaction except on drying ; then it came out perfectly. A piece made from a violet solution of half the strength showed a little; this acid rseemcd therefore to be close upon the limits of sensibility for an immediate reaction. It will also bk noticed that the more weakly colvred paper was slightly more sensitive ; on drying the darker paper shows as well o r better,
Tlie acid \vas tlilritccl to one-fifth its fornicr attwgtli or eight. hiinclretlis of oiie per cent. I now ndoptcd the foliowiiig way of opemtiiig: A convex cover was pl:ieetl oil :L water h t h , tlie water i i i \ v i i i c . I i was lieatcil to boiling; c.avli picbee of 1~:ip~'r as tlil)l)(!d w : i ~ laid O I I the ulil)('r ('on\-es stirfacc of tlie covcr; this clried i t i n about one iniiiiite; i n practice this will be f ' o i i ~ i c l :it1 e lleiit w:ty of iisiiig tile ] J i l l ) C r . '171~ stantlard paper dipped oticc n i i d dried sliowed the reaction, but iiot strongly; n second dippiiig and drying broaglit it out pel.fectly; n third trc,:itnient ~n:icle tlic reactioii still strongel.. \\'lien n 1Japel' colored by this weak acid was di;)ped a secori,l time the previous change of color was iiitlisceriiible iintil it 11;ttl drietl again. The acid was reduced to four-hundredths of one per cent.; t l l c . papel. j u s t slio\vcd tlie reaction after one dipping aiid dryirig : ; I sec o n i1 t rea t men t dcv clop ed i t 1)r r fee t 1y l'lic acid wns nest i~cduceilto t w o hundretlths of oiie per c e l l t . strc.iigt11; t.lie reaction appeared after three to five ti'eatrnents b i c t very faint I y . . l l ~ ) uthe t same results were obtained with sulpliuric acid of' C(JF r c > p~iicIirigstrengths. 1 t ~ ( ! r,ci.ics of euperirnents indicates pretty clorely the liniits o f scrisitiyciiess; drying tile l ~ p e~rn n i i u be t t6o strongly insisted I C ~ M J I I ; ill~1
