First and foremost a one and a half year old baby should not be on a bottle. It is very easy and that is why baby is refusing solids. Discontinue the use of the bottle completely so that the habit is broken. There will be a lot of tantrums and crying and it may seem like torture for you but over a few days your little one will understand and will start trying solids. In the mean while offer milk from a glass or a sipper cup.