This answer says that salt is considered poisonous to dogs. Additionally, the site linked in that answer states:
The use of salt to induce vomiting in dogs and cats is no longer the standard of care and is not recommended for use by pet owners or veterinarians!
If I catch my dog eating something poisonous (like chocolate), how can I induce vomiting?
I would then take my dog to the vet, but it's over 30 minutes to the ER vet from my house, and I think it's better to get the chocolate out quickly than let him digest it for 30 minutes.