This harmonica was made some time in the 1930s by the F.A. Bohm company, although the maker's name doesn't feature anywhere on the instrument. It is the instrument covered by German Patent 470354 and as you can probably tell from the shallow mouthpiece and the unusual placement of the button, this instrument is somewhat different from the Hohner chromatic design that came to dominate the market. Removing the covers makes it clear how it works:
The upper reedplate carries 20 blow reeds, with a pair of reeds to each chamber of the comb. One of each pair is a note from the C scale, the other a note from the C# scale. Above the reedplate is a slotted plate that allows only one of those reeds to sound at a time. This plate is held in position by a spring under the button. In the resting position, only the notes of the C scale are allowed to be sounded; pushing the button moves the slots to uncover the C# reeds and prevent the C reeds from sounding. On the underside of the comb, things work similarly, except in this case the slotted plate remains stationary and the reedplate with the draw reeds slides back and forth as the button is pushed.
This is an intriguing approach to chromatic harmonica construction, but it has one major drawback. As with the Bahnson Overblow harp, if you push the button as you are actually sounding a note, the sliding plate can easily snag a reed as it moves. This means it is impossible to play trills and get smooth legato between notes, things we take for granted with what is now the standard slide chromatic design.
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