Patent GB-651217-A (GB)
Title: Improvements in or relating to the colour testing of liquids and particularly the determination of the chlorine content
IPC: G01N21/29
Filed: 1948-02-07
Abstract: 651,217. Comparing colours. WALLACE & TIERNAN PRODUCTS, Inc. Feb. 7, 1948, No. 3642. Convention date, Feb. 27, 1947. [Class 97 (i)] Apparatus in which the colour of one of two liquid samples may be compared by a viewer with the colour of a third liquid sample seen through a colour standard selectively placed before the third sample comprises a movable device having a base and vertical walls and having fixed therein two chambers for the said two liquid samples, the device being held in one of two alternative positions by a socket-like holder in the apparatus to locate one or other sample for comparison with the third. The apparatus is described as applied to the orthotolidine-arsenite test for determining the chlorine content of water and as shown in plan in Fig. 4 comprises a window 46 admitting two beams which pass respectively through apertures 47, 50 in the casing and are conducted by prisms 18, 19 to a prism or reflector 20 by which they are directed to an eyepiece (not shown) for comparative viewing. A disc 25, Fig. 3, has coloured apertures 31 brought by rotation selectively into alignment with the aperture 47, and a central free aperture 30 in alignment with the aperture 50. A glass container 39 filled with the liquid under test is placed behind the aperture 47 and a carrier 40 containing glass containers 44, 45 containing the liquid to which the various reagents have been added is located in the casing adjacent the aperture 50. This carrier has two pairs of diametrically-opposite holes so that in the position shown one pair of holes registers with the aperture 50 so that the colour of the liquid in the container 45 may be matched with a colour on the disc 25, seen by light which has passed the control liquid in container 39. The carrier is then removed, rotated and replaced so that a similar measurement may be made on the liquid in the container 44. In a modification the carrier 40 is pivoted to the apparatus so that the containers 44, 45 may be interchanged, or the containers may be located one above the other and changed by a sliding movement. Instructions for using the apparatus may be printed upon the casing and on the carrier 40. In operation for testing the chlorine content of water three samples of the water are taken. Into the cell 39 are then placed, in order, an arsenite solution, the water and the ortho-tolidine solution. The resultant colour of this cell is thence due to substances other than chlorine or chloramine in the water. This cell acts, therefore, as a control. Into the cell 45 are placed, in order, the ortho-tolidine solution, the water, and then immediately a sodium arsenite solution. The colour of this cell is not influenced by the chloramines present so a comparison of the colours of cells 45 and 39 gives a measure of the free chlorine present. Into cell 44 are placed, in order, the orthotolidine solution and the water and a colour comparison gives the total of free chlorine and of chloramine when the amount of the latter present may be deduced. Specification 564,799 is referred to.