Johnsons of Hendon LTD. Comparator Test Books

Dug this little treasure up whilst packing my house up for the big move šŸ™‚

In excellent condition, from the famous photography supply company Johnsons of Hendon.

I estimate this box of test books is from the late 1940s.

Here’s a little description from a 1947 volume of Nature:

“WE have received from Messrs. Johnson and Sons, Manufacturing Chemists, Ltd., Hendon, London, N.W.4, samples of two kinds of test papers. These are made up in small books like litmus papers. The Universal Test Paper for the measurement of pH, values provides ten colour matches in steps of 1 pH from 1 to 10, with an accuracy of 0.5 pH, the appropriate colours being printed inside the covers of each book. The Comparator Test Papers provide a higher degree of accuracy, to 0.3 pH, inside narrower ranges, in four kinds from pH 3.6 to pH. 10, the colours being again printed inside the cover. The papers can be dipped into the solution, or the latter applied by a glass rod. We have tested both kinds of papers with buffer solutions and have found the colour changes to be as stated. They should be very useful to chemists, biologists, physicians, and workers in various industries, when a rapid and reasonably accurate method of measuring pH is desired. Messrs. Johnson also make a wide range of other test papers and supply a special grade of litmus in the form of granules free from the usual fillings of gypsum or calcium carbonate and requiring only extraction with water to produce an indicator solution. The firm, is investigating supplies of lichens from various parts of the world in attempts to produce a high-quality litmus. It is interesting to note that the firm was established so long ago as 1743.”

Indeed, I found this in one of the hospitals I studied at a couple years back.

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