The most notable of these was The Threatened Swan by Jan Asselijn, which became the first painting purchased by the director of the Nationale Konst-Gallery, Alexander Gogel.

It was marked to make it a political allegory of the patriot hero Johan de Witt who was murdered by orangists.

Since Roos was known for his patriotic politics, it is quite possible that he marked the painting himself when he bought it in 1800, though the estate sale catalog already mentions that it is an allegory of Johan de Witt.

The collection was moved to the former Prince William V Gallery, now part of the museum known as the Gevangenpoort.

His son Cornelis François Roos continued his art dealership and gallery after his death.