R. Yehudah says if someone lends money on a Mashkon he is a Shomer Chinam and if he lends fruit on a Mashkon he is a Shomer Sachar. (1)
Shmuel says if someone lends his friend a thousand Zuz and he receives the handle of a sickle for a Mashkon if the Mashkon is lost he may not collect the loan at all.
R. Yitzchak says that a Ba'al Chov is Koneh a Mashkon if it was given after the loan already took place.
A Shomer Aveidah is a Shomer Chinam according to Abaye, while R. Yosef holds he is a Shomer Sachar. (2)
R. Eliezer holds if a Mashkon is given at the time of the loan and the lender uses the Mashkon and subtracts the usage from the Chov it is not a Mitzvah that he lent him money since he is benefiting and therefore he is a Shomer Chinam.
R. Akiva holds even though the lenders uses the Mashkon it is still a Mitzvah that he lent him money and he is a Shomer Sachar because the Mitzvah is regarded as his Schar (wages).
If a Shomer moved the jug that he is guarding from place to place and it breaks whether he is a Shomer Chinam or a Shomer Sachar he swears that he was not negligent and he is Patur according to R. Meir. (3)
R. Yehudah says that a Shomer Chinam swears and he is Patur while a Shomer Sachar must pay. (4)
R. Eliezer says both a Shomer Chinam and a Shomer Sachar swears and they are Patur; however I don't understand why they are Patur with a Shevu'ah. (5)
If someone slips in the Reshus ha'Rabim and his jug breaks and he didn't sweep it up or his camel fell and he didn't pick it up he is Chayav for any damages that occur according to R. Meir because sipping is regarded as negligence.
The Chachamim hold he is Patur b'Dinei Adam and Chayav b'Dinei Shamayim because when someone slips is not regarded as negligence.
A BIT MORE
1. If he lends fruit he is a Shomer Sachar because fruit is a perishable item.
2. R. Yosef holds since guarding an Aveidah is a Mitzvah the Mitzvah is regarded as his Schar.
3. R. Meir holds when someone slips it is regarded as an Ones and even a Shomer Sachar is Patur
4. R. Yehudah holds that slipping is not negligence but it is on par with Geneivah and Aveidah and therefore a Shomer Sachar is Chayav and a Shomer Chinam is Patur.
4. R. Eliezer holds that slipping is not an Ones and therefore he doesn't understand why a Shomer Sachar is Patur and he also holds that sometimes slipping is negligence such as if he slipped on level ground and even a Shomer Chinam should be Chayav.
A Shomer Aveidah is a Shomer Chinam according to Abaye, while R. Yosef holds he is a Shomer Sachar since guarding the Aveidah is a Mitzvah and when he is occupied in caring for the Aveidah he is doing a Mitzvah and someone who is occupied in a Mitzvah is Patur from another Mitzvah that comes his way and consequently he is Patur from giving a Perutah to a poor person. The Ritva asks that every Shomer should be a Shomer Sachar for this reason since he is doing a Mitzvah by guarding an item that belongs to his friend and when he is occupied in caring for the item he is Patur from giving a Perutah to a poor person. The Ritva answers that when a regular Shomer receives the item from the owner it is understood that he only wants to be a Shomer Chinam not a Shomer Sachar and it is as if he explicitly made a condition that he is only Chayav like a Shomer Chinam. However, a Shomer Aveidah and a Shomer of a Mashkon who received the item only by way of the Mitzvah that they did he has in mind that he will be a Shomer Sachar. Alternatively the Ritva answers that it is a Tenai Beis Din that he a Shomer Aveidah or a Shomer of a Mashkon is a Shomer Sachar even if he had in mind that he only wants to be a Shomer Chinam.
A LOST MASHKON
If someone lends his money on a Mashkon whether he lent money or fruit whether he was given the Mashkon at the time of the loan or after the loan took place he is a Shomer Sachar. It doesn't make a difference whether he explicitly stated that he is taking the Mashkon at its value or he took it Stam. Therefore, if the Mashkon is lost or stolen he is Chayav to pay and if the Mashkon was the same value as the loan he is Patur from repaying the loan and if the loan is more than the value of the Mashkon the borrower must pay the difference. According to someone opinions if he spoke out at the time of the loan that he is accepting the Mashkon for the entire loan even if he took a handle of a sickle for a thousand Zuz if he loses the Mashkon he loses everything. If the value of the Mashkon is more than the loan the lender must pay the difference to the borrower. (Shulchan Aruch CM 82:2)