AL\7-4LYTICiALE D I T I O S
194
.Voie-Hepp ( I ) obtained a product with properties of a nitrated phenol b y nllowing an alcoholic solution of trinitrobenzene t o stand for a short time with 2 mols of potassium hydroxide. Lobry de Bruyn ( 7 1 obtained 3,j,3,,j,.tetranitroazohenzenzene and dinitrophenol by boiling trinitrobenzene with dilute sodium carbonate or b y allowing the mixture t o stand ;it room temperature for 3 days. Sodium- hydroxide reacted similarly sIo~vIy a t room temperature.
acidification. I n such a solutioii the color change of broinophenol blue cannot be detected easily. Congo red is a sat,isfactory indicator in such cases. and good results were obtained by using it, for cklaIlge froIn red t o blue-violet is detected Jvit,h in the presence of a high concentratioll of the Droduct from trinitrobenzene. Seither Congo red nor bromophenol blue is as satisfactory as dirnethylaininobenzene as an indicator for adjusting the acidity before the initial tit'ration. The red color of Congo red in alkaline solution interferes with the end point of trinitrobenzene. If the final titration is made with bromo-
blue in the solution increases the difficulty of rPc(ogniZing
\-01. 2 ,
so.2
this Doint. so this indicator is not atlcled ulitil the solutioli is about neutral. A slight error is introduced by using one indicator for tlio initial adjusting of the aciditv of t,he So~LltiOllalid anflthW for tlie final tiGation. The err(jr t1iLls introduced, honevcr. does not exceed 0.1 per cent of XgO. I
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Acknowledgment
Ickiio\\-ledgmeiit is niade to the 1 1 0 ~C'lieinical C'IIIIIpany for the analyzed samples of niagi~esirunchloride -aIts used in the determinations. Literature Cited $ ~ ~ ; b ~r ~ n~ ~ ~ ~ a ~ (,on$ ~ . l p p~l C i lde r n , ,,1, t 3 ) Kolthoff, z , a n o y 6 . ailgem. C h t . m , 112, 11920). (4, m i t h o f f , Rec. I Y ~ L ' . citim., 41, 787 WXI.
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(91 U'illitntter a n d \Valdschmidt-Leitz, B e y , 5 6 , 488 (1923)
Multiple Standard Colorimeter for pH Determinations' S. L. Leiboff BIOCHEMICAL LABORATORY, LEBAVON HOSPITAL. SEXUORK,S U
HIS coloriineter was especially designed for inatchiiig colors of uiikno~vnsolutions where a single standard
T
cannot be used, particularly in colorimetric hydrogenion determinations of wide range.
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Figure 1-Box
for Standard Bottles
'C'sually such determinations are done in test t i i h i i i a block comparator where the tubes are placed side Iiy bide antl the color differences observed. I n the colorimeter here described all the standards are contained in sinall, rcctangular bottles of uniform size with two opposite parallel plane sides! t,he distance between ivhich is uniform in all the hottles. This allows t,he passage of light through equal depths of solution. T h e standard bottles are placed close together in a a black rectangular box. (Figure 1) This box contains circular fenestrz on two opposite sides parallel to each other. E a c h bottle fits snugly between a pair of fenestrzep,thus allowing the light to pass bhrougli a uniform depth of solutioii u-ith all the standards. Figure 2 s h o m the colorimeter \\-it11 the standards in place. It consists of compartment A ! which contains two mirrors, JI and JI', placed a t a n angle of 1 5 degrees aiid parallel to each other. Mirror -11' is half the size of mirror JI. The cylinder B carries a magnifying lens, L, aiid an eyepiece: E. Received December 13, 1929. Very suitable bottles are Kos. 31.190 and 31,192, Eimer 8r Amend Catalog, 1927, p. 706. These bottles are used for spectroscopic work and a r e inexpensive. 1 2
To facilit,ate the reading the reading tuhe itself may IIC sluped, with t,he mirrors tilted a t an appropriate angle. For the determination of pH the following arrangement is used: I n compartment C are placed the unknown) standards, and compensators. Bottle 1 contains the unkiiowi iolutioii with the appropriate indicator. Bottle 2 contains di,tilletl water. Bottle 3 contains the unknown solution, hut without indicator, to compensate for cloudines aiid color of the iinknown. The box containing the staiidards i: placed a t 1antl is moyed along the stage S horizontally by means of a rack aiid pinioii, R P , with the thumb screw T,5'. Thie Iiox is m o d along on the stage while the operator is looking t h r ( i u g 1 i the eyepiece until the E c l o s e s t match is obt a i n e d b e t w e e n t>he standard and the un-B known. T h e light p a s h i ~ i gthrough the feiiestrze F and F ' is reflected uplvard by the in i r r o r s-in i I' r o r M' c o y e r i n g one-half of mirror JT, antl p r o d u c e s , ~vlieiiv i e w e d through the eyepiece, the effect of a c i r c l e , o n e - half representing the itaiidard and the other half representing the unknown. Comparisons may be niade by artificial light by placing a few sheets of tissue paper between t h e s o u r c e of l i g h t TS and the colorimeter in RP Order to diffuse the Figure 2-Colorimeter w i t h Standards light. i n Place
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