The curcuma test paper was found by the authors to be available for the purpose of detecting directly boric acid added to Kamaboko as preservatives. A modified method was devised not only to be applied directly to Kamaboko without laying it in ashes but also to detect boric acid sensibly up to the concentration of 0.02% in Kamaboko.
The modified curcuma test paper is prepared as follows: Dissolve 0.04g. of curcumin and 3g. of oxalic acid in 100cc. of acetone, then add conc. hydrochloric acid to the solution at the rate of 0.8cc.to 5cc. of it. Soak a qualitative filter paper into the above solution and dry at the room temperature.
In order to detect boric acid in Kamaboko, press a suitable size of Kamaboko section on the modified curcuma test paper, and allow to stand for 5min. or heat at 50°-60°. When red colour (the colour of curcumin-boron complex) is detected on the yellow test paper, it can be judged that the Kamaboko contains boric acid. The level of boric acid contained can be estimated approximately from the intensity of red colour.