Your cut-off date now appears to be 1854:

Name: m salt and son dissolved 1854.JPG Views: 108 Size: 49.7 KB

After that the company name changed from M. Salt & Son to simply Salt & Son. They won an award under this name in 1873:

Name: salt and son 1873.jpg Views: 100 Size: 43.1 KB

and lasted until 1883:

Name: salt and son 1883.JPG Views: 100 Size: 80.8 KB

After which the name changed again.

Regards,
Neil