Notes on the “Depression Plant.” O. J. THIES, JR.

The depression flower, a chemical growth consisting largely of salt on coal, brick, twigs, etc., has attracted widespread attention. Many explanations have been offered for the growth, but heretofore all have omitted the bluing called for in formulas. (Common formulas call for salt, bluing, water and an alkaline substance.)

The growth will not occur on brick, coal, etc., when pure salt is used alone, nor when blue ink, liquid bluing, ferri ferrocyanide, saponin, sodium bicarbonate, sodium carbonate, potassium ferrocyanide, sodium sulphite, copper nitrate, copper nitrate with copper ferrocyanide, mercurochrome, potassium chromate, ammonium hydroxide, lime, magnesium carbonate, sodium dichromate, and ferrous sulphate, respectively, are used with the salt. Potassium dichromate, potassium cobalticyanyde, and sodium cobaltocyanide, respectively, with salt produced a suggestion of growth, but nothing to be compared with that of the depression plant.

Growth was produced when bluing was mixed with the salt in the presence of some alkali, and in almost every case (except in the presence of deliquescent substances, strong acids, and strong alkalis) when salt was present with potassium ferrocyanide, sodium ferrocyanide, ammonium ferrocyanide, or any other substance supplying as much as 0.02% ferrocyanide ion. On tenth of this amount is insufficient to cause growth of the plant. Best results are obtained with about 0.1% potassium ferrocyanide. Too much ferrocyanide interferes with the growth.

The success of the formulas using bluing is to be attributed to the fact that added alkali, soda or ammonia, or alkali in free-flowing table salt used, reacted with the ferri ferrocyanide of the bluing to produce a soluble ferrocyanide.

Only two substances, potassium chloride and potassium bromide, were found which could be substituted for salt. These behaved much as salt did, and potassium bromide even showed some tendency to grow in the absence of a ferrocyanide. The following produced no growth with or without ferrocyanide: Deliquescent substances, ammonium chloride, sodium iodide, sodium bromide, potassium iodide, sodium fluoride, ammonium nitrate, sodium nitrate, sodium sulphite, borax, trisodium phosphate, sugar, sodium carbonate, and magnesium sulphate.

The growth of the “plant” is dependent on the evaporation of water, leaving behind particles of salt, which are mixed with a small amount of ferrocyanide. The salt particles do not appear typically crystalline, and frequently the growth is tubular, like stalactites.

Potassium ferrocyanide is abnormal; in a number of its properties. One of these abnormalities is the fact that its beta form will grow into a depression plant when treated with water and in the absence of salt, whereas the alpha form will not grow into a depression flower. However, either the alpha or beta form will cause salt to grow.

Explanation of the growth of the depression flower was sought in surface tension determinations of solutions of salt and ferrocyanides. Results were so erratic, however, that no conclusions could be drawn. Osmosis and capillarity are both probably intimately connected with this phenomenon.

The results of our experiments lead to the conclusion that the ferrocyanide ion is unique and specific in causing sodium chloride to grow into depression flowers.