There are many interesting observations that can be made about the horn playing style in the class led by Merck at the Brussels Conservatoire from the mid-1860s onwards, and these alone could easily be the subject of a comprehensive study. I limit my comments here to three general observations:
The presence of a large amount of high-quality players in Brussels at that time encouraged the writing of a considerable number of high quality pieces for the horn. A fine example are the 3 octuors by Léon Du Bois (published by Ostermeyer Edition). They all share a common language in terms of musical texture, and have common aspects in structure, and common technical features such as unaccompanied cadenzas and stopped note passages. Strikingly, the horn parts never call for the extreme high range of the instrument, with the range limited mostly to the top A. However, the extensive repertoire list of pieces performed at the Brussels Conservatoire exams contain some exceptions on this rule.
Secondly, one has to consider that in Merck's class the natural horn was still practised, although not as a primary instrument. The horns used in the class were mainly three valve piston horns and the most common models were certainly the horn models by Brussels builders such as Mahillon (the official "fournisseur du conservatoire” - supplier of instruments to the conservatoire and director of the musical instrument museum) as well as Van Cauwelaert. The conservatoire owned from 1874 four horns with six independent valves by Adolphe Sax, an instrument promoted by Merck by means of publication of a method and a series of studies. It is uncertain though if they have ever been used significantly in the horn class, as they were primarily purchased for use in the orchestra of the Société des Concerts in order to play music by old masters.
As a third and most important point we should note that the way the instrumental courses were organised encouraged the development of a particular and school-based playing style and sound: the students were encouraged (and sometimes obliged) to be present several days a week, and as such attended the lessons of most of their fellow students. One of the effects of this system was that students were completely soaked in the specific playing style of their teachers and fellow students, and the isolated context of the classes meant they were not or only rarely exposed to musical influences from elsewhere. A side effect was the development of certain repertoire, which was sometimes completely different in Ghent, Liège or Brussels. Also, this isolation was ideal for protecting the own job market, as 'intruders' would simply not stand a chance as they were likely to play in a different style and perform different material. It is striking to see that this practice only disappeared during the 1960s, and only rarely exists to any extent today (see, for example, the Vienna Philharmonic).
It in this setting, the Mélodie of Van Cromphout is a fine example of the colourful, almost impressionistic, Morceau de Concours for horn used in Merck's class, and the particular harmonic power of the lyrical style repertoire.