On Julius Planer’s 1861 paper “Notiz über das Cholestearin” in Annalen der Chemie und Pharmacie

In his celebrated article [1], widely known as the first publication on liquid crystals, Friedrich Reinitzer among others gives a proper credit for his finding to the work of Julius Planer [2] published twenty seven years earlier. In particular, Reinitzer wrote: “Thus, Planar reports that cholesteryl chloride displays a violet colour during cooling from the melt which vanishes again upon solidifying. Raymann reports similar observations on the same substance. Lobisch reports that cholesterylamine when melted displays a bluish-violet ‘fluorescence’ and also mentions the occurrence of the same phenomenon in the case of cholesteryl chloride. I myself observed a similar phenomenon in cholesteryl benzoate, and Latschinoff reports for the silver salt of cholesteric acid, which is formed by oxidation of cholesterol, that it turns steel blue when melted, which fact is probably to be explained in the same way”. The selective reflection in cholesteryl chloride by Planer in 1861 and in cholesteryl benzoate by Reinitzer in 1888 unambiguously proves observation of the cholesteric liquid crystal phase. However, neither Planer nor Reinitzer did not pursue studying liquid crystals further. The research was continued by Otto Lehmann, who realized that this is a new phenomenon and started its systematic study resulting in the paper [3] published in 1889. Many scientists cite only the Reinitzer’s article when referring to these pioneering observations. In the modern literature, several textbooks give credit for the observation of liquid crystalline state to Planer, some to both Planer and Reinitzer, whereas some give credit for this important observation to Reinitzer alone. Interestingly, both Reinitzer [1] and Planer [2] papers originally were published in German. However, an English translation of the Reinitzer’s article was already republished in 1989, i. e., after hundred years [4]. The goal of this note is to introduce the Planer’s 1861 paper to a wider condensed matter community. To show the importance of this paper, in what follows we present the selected citations of the Planer’s observations that we were able to locate in modern literature, in particular, in some of the textbooks dedicated to the history of liquid crystals discovery. To proceed, let us first say a few words on this Planer’s 1861 paper [2] (a translation of this paper into English can be found in this issue). From the paper one can learn that Planer is primarily