COPPER SALTS AS LIGHT FILTERS.
I11
BY W. V. BHAGWAT AND N. R. DHAR
Part I11 Landolt’ states that crystal violeto5 B.O. 0.005 grm. in roo c.cs with 15 gms. of CuS04.jHz0 transmits 4482 A in two centimeters thickness. Pots$sium dichromate and CuS04.5HzO are known to transmit 5769-5790 A. TT’inther* observed that a comkjnation of cupric chloride with potassium chromate transmits 5400-5050 A. Chromic acid with a saturated solution of copper nitrate is known to eliminate blue violet rays. \Ye have studied the combination of methylene blue, crystal violet, potassium chromate, potassium dichromate and chromic acid with copper salts as light filters both in the visible and ultra violet.
Methylene Blue The methylene blue is found to absorb the visible portion of the spectrum on the side of the red, a property, which is similar to that of copper salts. Hence methylene blue cannot be advantageously used in combination with copper sulphate or copper nitrate, which has absorption only towards the red side of the visible spectrum. However, methylene blue can be combined with cupric chloride, Khich possesses absorption both in the red and violet ends of the spectrum. = Wave length in b units. e = extinction coefficient. ’%T = percentage transmission. (I)
Methylene blue Conc. -0.0232 grm. in IOO c.cs of water. Cell one centimeter thick. j400-7000 5380 j310 5040 5180 e W 2.6 2.3 2.15 2.05 %T 0 0.25 0.50 0.70 0.89 x 4850 4720 4590 4470 e 1.38 1.04 0.84 0.66 %:cT 4.1 9.1 14.4 21.8
iMethylene blue Conc.-o.o116 grm. in I O O c.cs of water. 5380 5180 5000 5600-7000 5 5 2 0 e W 2.0 1.46 1.08 0.86 1.0 3.4 8.3 13.8 %T 0 4590 4470 x 4720 0.34 0.27 e 0.54 ?&T 28.8 45.7 53.7 “Daa optische Drehungsvermdgen” 2nd. Ed., p. 387. * Z . physik. Chem., 41, 169 (1902).
5000
70 1.9 I .
(2)
4850 0.72 19.05
2402
W. V. BHAGWAT AND N . R. DHAR
+
Methylene blue (3) Cupric chloride Conc. 9.285 N Thickness of each substance = I cm. in I O O c.cs. 7000-5220 5150 5080 j020-4000 e m 2 .j 2.j m
%T
0
0.31
0.31
0.0232
gms.
0
(4) Cupric chloride Conc. 9.28jN +Methylene blue 0.0116gms. in I O O c.cs. X 7000-5440 j22O jIs0 5080 5020 4980-7000 e m 1.9 1.90 2.0 2.15 W
%T (5)
0
1.2
1.2
I .o
0
0.70
Cupric chloride Conc. 4.642 N +Methylene blue 0 . 0 2 3 2 gms. in 7000-5220 5020 4840 4700 4580-4000 m 1.9j 1.85 2.1 X e %T 0 1.1 1.4 0.79 0
I O O c.cs.
(6) Cupric chloride Conc. 4.642?i +Methylene blue 0.0116gms. in I O O c.cs. X 7000-5440 5 2 2 0 5020 4840 4700 4j80-4000 e m 1.55 1.26 I 2 I.jj m %T 0 2.8 5.4 6.3 2.8 0
These results are summarked in the following tables:Conc. of methylene blue 0 . 0 2 3 2 gms. in I O O c.cs of water o 0116 ” 0.0232
”
o.0116
‘I
Conc. of cupric chloride 9.285 K
Range of transmission
9.285 S 4.642 X 4 642 N
5440-4980
5220-jozo
5220-4580
A
7CT (Maximum) 0.31 1.2
a$
5440-4580 A
1.4 6.3
These results clearly point out that, although the combination of cupric chloride and methylene blue, transmits short ranges, the amount of transmission is very low. This difficulty cannot be avoided by decreasing the concentration of any or both of the constituents, because the range of transmission is much widened on diluting the substances and even then the percentage transmission is less than that of 9.28j 9 cupric chloride alone. Although a concentrated solution of methylene blue shows only one-sided transmission, that is, towards the violet, when the solution contains 0.0058 grm. in I O O c.cs of water, it begins to transmit the red radiations. I n other words, it has transmission in both the sides of the visible spectrum in dilute solutions like methyl violet. Concentrated solutions of methylene blue can be combined with potassium chromate, to give a short range of absorption on the violet side. Concentrated solutions of potassium dichromate have high absorpt,ion on the violet side extending as much as to absorb all the visible
2 403
COPPER SALTS AS LIGHT FILTERS
region transmitted by methylene blue and hence a combination of potassium dichromate and methylene blue has little advantage as a light filter. Dilute solutions of potassium dichromate with methylene blue transmit the regions similar to those transmitted by a combination of potassium chromate with methylene blue.
(I)
(2)
Methylene blue Conc. 0.0232 g m . in Thickness of each substance = I cm. 5020-4000 5080 5150
c.cs
IOO
+ K2Cr04.Conc. 3.68 N
m
2.4
2.3
2.2
%T
0
0.39
0.50
0.63
Methylene blue Conc. 0.0116 gms. in x 5020-4000 5080 5150 e m 1.70 1.50 %T 0 1.9 3.1 x 5440 j 5 2 0-7 000 e 1.95 a3 %T 1.12 0
5300 2.4 0.39
5220
e
5370-7000 m 0
c.cs-K2Cr04 Conc. 3.68 N. 5220 j3OO 5370 1.40 1.44 1.55 3.9 3.6 2.8
IOO
Crystal Violet Crystal violet has properties similar to those of methyl violet, transmitting both red and violet sides of the visible region and absorbing the intermediate portion. It can, therefore, be combined with cupric salts to transmit only the violet side or with potassium dichromate to transmit only the red end. Our results with crystal violet are recorded below: (I)
Crystal violet Conc. 0.0081 grm. in
IO
c.cs of water.
x
6600
6280
6180
6070-5020
e
0.05
1.1
2
.o
m
I .o 43 40
0
%T
x e
%T
89.1 4580 0.65 22.3
7.9 4460 0.43 37.1
4840 1.75 1.7
4700 1.18 6.6
0.20
63. I
As cupric nitrate and copper sulphate have only one-sided transmission and that also in the same region as that of methyl violet or crystal violet, a combination of crystal violet and copper nitrate or sulphate will only decrease the intensity of the incident light without any gain. h combination of crystal violet with cupric chloride of concentration 9,285 K absorbs all the visible. Crystal violet conJaining 0.0040 grm. in I O O c.cs water transmits the regions from 5960-7000 A and 5220-4000 -k. A solution of crystal violet having 0.0016 grm. in IOO c.cs water transmits all the region of visible spectrum without complete absorption anywhere and having maximum absorption in the ycllow.
W . V. BHAGWAT A S D S . R. DHAR
2404
(I) Crystal violet-0.0016 grm. in Thickness of each substance = X 'joOo-jj20 5440 5360 e m 2.15 2.05 %T o 0.70 0.89 4960 4900-400 e 2.2j m %T 0.56 0
c.cs +cupric chloride-Conc. 9.285 2;. cm. j290 5220 jIjo 5020 2.oj 2 . 0 1.9; 2.oj 0.89 1.0 1.1 0.89
IOO
I
Thus the combination is not so suitable as cupric chloride alone. (I)
(2)
+
Crystal violet Conc. 0.0080 grm. in IOO c.cs K2Cr2071.16 j K. Thickness of each substance = I cm. X 4000-6070 6100 6280 6380 6490 6600 m 2.05 I .34 0.72 0.29 0.IO e %'oT 0 0.89 4.5 19.0 j I . 2 79.4 Crystal violet Conc. 0.0080 grm. in 6600 6490 6380 0.23 0.68 0. I O 20.8 58.8 %T 79.4
X e
IOO
c.cs K2Cr20i0. j 8 2 S . 6280 6180 :Jo;o--.;coo I
,32
4.7
2 9
.og
x
89
0
Thus for the transmssion of red from 6180-7000 .?, a combination of crystal violet with potassium dichromate is a suitable filt>er. However the range of transmission is rather long. (I)
Methyl violet 0.100 grm. in I O O C,CE 4- ki2Cr2071.165 K. Thickness of each substance = I cm. A 0490 4000-6280 6380 6600 6730 e co I . 50 0 98 a. 52 0.25
%T (2)
X e
10.4
Methyl violet 0.100grm. in 'coo c.cs 6490 4ooG-6280 6380 co
%T X e
%2'
I
0.100grm.
4000-6280 cc 0
.q8
0.98
33 ' 1
0
Methyl violet
(3)
3.:
0
6380 0.48 33.7
10.4
in
100
c.cs
6490 c
,98
10.4
30,z
+ K2Cr&i
j 8 .8
56.2
0.116j
6860 0.23
N.
0600
6730
6860
0 .52
0.25
0.23
30.2
56.2
j8.8
+ KpCrOi 5.889 ?; 6600
6730
6850
0.50
0.2:
0.25
j i
.6
56
2
58.8
Thesr results indicate one interesting fact that the methyl violet comhmation with potassium chiornate anti potassiurn dichromate 01 different concrntratiuns transmit not only thc wme range b u t also the same amount of light.
COPPER SALTS AS LIGHT FILTERS
2405
This fact is also observed in case of crystal violet. V e l have shown that potassium dichromate and potassium chromate have practically the same and very little ahsorption in the red and hcnce when combined with methyl violet or crystal violet exert the same influence. W r a t t m filtcrs S o s . 89, 70, ~ I A 6, 9 ~ 1 , and 91 are comparable with the above combinations. Of thew Wratten S o . j I X has much less transmission and still longer range. Althaugh filter Kos. 89.1 and 91 have very short ranges, they have very loiv percentage of transmission. T r a t t e n filters Kos. i o and 89 are decidedly superior both in respect t o short range and high transmission. Chromic Acid and Copper Salts Chromic acid \vith a saturated solution of copper nitrate is known to eliminate blue-violet rays. Like potassiuni chromate and dichromate it has the nhaorption in the violet side of the visible spectrum. A pure sample of chromic acid was obtained by dissolving Rlerck’s chromic acid in watcr and filtering through glass wool. The chromic acid was precipitated from the solution by adding fuming nitric acid, which w:is removed by slow evaporation on a water bath and finally by keeping it over solid caustic potash. The highly concentrated solutions (conc.-:.66 S)of chromic acid is found t o a h a r b all visihle and ultraviolet light rays. Dilute solutions of chromic acid transmit the same regions as those transmitted by potassium chromate and dichromate. The advantage of chromic acid over potassium chromate or dichromate consists in its greater solubility and hence in its greater powrr (If absorpticn. V h e n a concentrated solution of chromic acid is diluted, the c,!ivnpe in complete absorption instead of being gradual is sudden and henct. suitable altcrations in it: concentration does not offer much advantage over potassium dichromate. The following tables represent our rcsults with chromic acid of various concentrations and its combination n-ith cupric nitrate solutions of different strengths: (:hroniic acid Conc.--;.666 1. 400o.-j600 j8;o 6160 e m ~.~jii 0.86 13.8 %l’ 0 4. I
(r)
X
Chromic, arid Conc.--2.833
(2)
X
4ooo-~oRo j b o o 1.44 X
e YcT (3)
o
,3.5
0.53
31.6
S. j8;o 0.50
3i.h
6160 0.38 41.6
6;40 3 . z j .tlic a h 1 - e combin:it ions arc usrful fnr the tmnxe mission of the regions 5 ~ z o - ~ ~ j ooZo-552o .I and ;a:o-s!ibc .i.~ 1 1ucefu1nes.q of such conibinations co 3 in the fact that potassiurii tliehromntt~, potassium chromati, a i d clirciiri d ciit cjff the violet side and the copper salts the red side nf the visiLle rppctrum, m t l hcncr suitablt. coiiibir1:ttions of cupric s n i t s nrid n rhromnte give u.- filters cE con.\-cnient range in the visible Fpeclrum. V ~ ec:m, howewr, cuiitrol only one of the two f;ictors, the transmis~ionor the range. I t is inqmsiblo t o shorten the range nithout tlie loss of transmission, Ultraviolet Absorption Any conerritration of pot:^, ,I,un dichrornntc greater than O . O O Q ~ ?X Libs o r h all the ultrnviolpt, whiic the, concentration 0.000942 is found to transmit ppcr arc. T h u s the combinations of all the ultraviolet ubtained i'roni potassium dichromate with copper Its transmit only the visible p p i o n of the spectrum. Cupric nitrate comb ation transmitting 5ozo-5jzo A can be compared with \\-ratten filtprs SOS.54, 6 2 , and 74. XI1 of them have a longer Oi O although \Yratten S o . 6 2 and 7 4 are more range extending from ~ O O O - ~ ~ . useful on account of their greater trnnsmission which is I jTc (maximum) of the incident light.
COPPER SALTS AS LIGHT FILTERS
2 409
Potassium Chromate and Copper Salts The principle of combining potassium chromate with copper salts is the same as t h a t of combining potassium dichromate and cupric salts and that is t o cut off the violet side. From the measurements of absorption of potassium chromate and dichromate we’ have shown t h a t for the same concentrations potassium dichromate has a greater absorption limit than potassium chromate. Hence, potassium chromate has no advantage over potassium dichromate combinations. Even the concentrated solutions of potassium chromate do not shorten the range of transmission of cupric chloride (9.285 X) but diminishes the intensity of the transmitted light. This will be clear from the following results:Cupric chloride Conc. 9.285 S Thickness of each substance
(I)
X e %T
x
4000-5020 3 :
0
+ Potassium chromate j.889 S = I
j220
5290
1.26
1.14
5360 1.14
j440 1.32
7.2
4.7
5.4
7 . 2
5680 0.70
e
I.jO
j600 1.80
%T
3.2
1 . j
j j 2 0
cm.
5jio-jooo
? . I
X
0
The rangc of transmission of cupric chloride 9.285 S alone is 5 0 2 0 - j j j o A and the maximum percentage transmission is I O . Thus the combinations of potassiilm chromate with copper salts have no advantage o w r combinations of potassium dichromate and copper salts. Ultraviolet Absorption Concentrations of potassium chromate greater than 0.05889 S :ibsorb aLl the ultraviolet. A concentration of 0.01 178 S transmits only 3036-3248 -1 of the ultraviolet. I t is observed that :iconcentration of 0.0011j 8 of potassium chromate trans?its all the ultraviolet with a trndcncy of absorption in the region j z & 4 o o o .1. Thus pot ium chronxtte seems t o h a i c a srlective a!xirption in the region 3248-4000 ,;. I t has bpen shon-n by Dhar’ and by Bhagwit and Illiar‘j that chroniic acid in dilute solutions appears to exist mainly as HCrO,’ and CrO1” ions and as C’r207” and HCr,07’ ions in concentrated solutions. This view is confirmPc1 froin the ultraviolet absorption of dilute solutions of chromic acid and potussium :hroniate, where they show a selectivc absorption in the region 32484000
&I,
Bhagwat and Dhar: J. Indian Chem. Soc., 7, 9x3 (1930). Z. anory. Chem., 121, 99 ( 1 9 2 1 ) ; .J. Indian Chem. Poc., 5, 5 8 j (1928) .J. Indian Chem. Por., 6, 781 (1929): 7 , 913 Ir930).
2410
W. V. BHAGWAT AND N. R. DHAR
S-arY Combinations of cupric salts with crystal violet, methylene blue, potassium chromate, potassium dichromate and chromic acid as light filters have been studied and the percentage transmission and extinction coefficients of these combinations have been determined. The ultraviolet absorption for the same has been obtained photographically. I.
2. The ultraviolet absorption by dilute solutions of potassium chromate, dichromate and chromic acid in the region 3248-4000 1,is practically identical. This behaviour is satisfactorily explained on the view point that chromic acid exists as H2Cr207@ HzCrOl and the equilibrium is shifted towards H2Cr207for concentrated solutions.
3. It has been shown that potassium chromate or dichromate exerts the same influence on the absorption when combined with methyl violet or crystal violet for the transmission of the red region. This is explained by the fact that both the salts have practically the same and very little absorption in the red.
4. Combinations of copper salts with potassium chromate, dichromate, chromic acid and other substances have been compared with Wratten filters and it is observed that copper sulphate has no advantage over either of the two copper salts, the cupric nitrate and cupric chloride.
5 . From our investigation we find the following solution light filters very convenient for photochemical investigations: Range of, transmission
Filter
One. 9.285 N Cupric chloride in I cm. thickness. Two. 4.891 N Cupric chloride 2 0 c.cs 30 c.cs of 2 0 7 5 ammonia in I cm. thickness.
+
4900-5770
Ai
4000-4590
A
4000-5000
-1
Percentage transmission (Maximum) 10
4.78
Three. 1.05 r\’ Copper sulphate 20 c.cs I O c.cs of 20% ammonia in I cm. thickness.
+
2 . 7 1 6 N Copper sulphate
Four.
+
grm. methyl violet in I O O c.cs. of water, each in I cm. thickness. 0.050
Five.
2.716 N Copper sulphate
+
0.010grm.
methyl violet in I O O c.cs. of water, each in I cm.thickness.
45.7
COPPER SALTS AS LIGHT FILTERS
+
Six. 7 . 2 4 4 K Cobalt chloride K i I o cupric chloride, each in I cm. thickness.
2411
;.
Line 2961 & the region 3248-74 A
Seven. 0.0116 grm. Methylene blue 9.285 X in I O O c.cs. of water cupric chloride, each in I cm. thickness.
-
+
Eight.
Crystal violet in water 1.165 N potassium dichromate] each in I cm. thickness.
1.2
0.0080 grm.
I O O c.cs. of
+
Nine.
0.10 grm. Methyl violet in c.cs. of water 1.16j potassium dichromate] each in I cm. thickness.
6070-7000
d
79.4
6280-7000
11
j8.8
5380-5870
.I
+
IOO
+
Ten. 6.087 N Cupric nitrate 1.416 N chromic acid, each in I cm. thickness.
1.2
+
Eleven. 5 . 5 2 7 N Cupric nitrate 0.5825 i Y potassium dichromate, each in I cm. thickness.
5290-5870 ' 4
+
Twelve. I 1.054 N Cupric nitrate 0.582 5 K potassium dichromate] each in I cm. thickness.
5020-5520
b
9.285 N Cupric chloride
Thirteen. 0.5825
K potassium dichromate,
each in
I
cm. thickness.
Chemistry Department, L'nzi'erstty of Allahabad, Allahahad, India. March 12. 1.931.
1.41
