Items are rarely "lost", and are usually just not shown in the item list. Go to Thomas Jefferson at the Graff House in 1776 AD and see if the prompt will tell him "I have the Declaration". Otherwise, the document (for whatever reason) is still in the hands of the merchant in 1387 AD.
The Graff House is where Thomas Jefferson stayed while writing the Declaration of Independence. On Time Tangled Island it is at 1776 AD, or 7 o'clock on the time device. When you bring the Declaration of Independence back to Thomas Jefferson, the salt rocks for 1387 AD (Mali Empire) are on the roof.
The Declaration goes back to 1776 AD (7 o'clock on the time device), and you will find the salt rocks (for the merchant of Mali, 1387 AD) on the roof of the house in 1776.
Take them to 1387 AD where their owner is glad to get them back. The Declaration of Independence draft can be found at the Timbuktu Inn to the far right at 1387 AD.
the timing device is a device that takes you back in time in time tangled island
On Time Tangled Island, click on the crab several times until he explodes. (Not to worry, he rapidly pulls himself back together.)
you go back to the LAB to go to the future.
You go back to the lab then to the future in the big time machine get to your house and get the medal!
If you click on him repeatedly, he will explode, then come back together.
After you travel back to the future to get the Island Medallion, return to the present to leave the island (just as you did after completing the items), by using the Lab selection on the time device.
On your first visit using the future machine, you get the time device from your future self, so that you can restore the items that are tangled in time. When you finish and get the Island Medallion, you still have the device. Set it to "Lab" and go back to Professor Pendulum's lab.
you do not lose it you use it to get something in the viking time to explode rocks in your way.
Be sure to leave any of the "challenges" on Time Tangled Island. If the time device still doesn't show up, reboot Poptropica to see if it will set you back to the start of 1593 AD.