Daniele took a number of photographs of the remains of the barrel bombs, some of which were published in the Daily Telegraph. He's now given me permission to publish the remaining 59 photographs online, the full collection of which can be found here.
The following pictures shows the remains of a cylinder that has a number of interesting features
This appears to be the same chemical barrel bomb featured in this video from Kafr Zita on April 18th
As I noted in an earlier post, det cord has been wrapped around the neck of the cylinder, shown below
It would appear the function of this is to blow off the end of the cylinder using the least explosive power possible, reducing the among of chlorine gas destroyed in the explosion. One photograph may show an example where this configuration has functioned as intended
Another interesting feature of the same barrel bomb is the metal bar with two large bolt which sits in front of the cylinder
The same metal bar and bolt assembly is visible in a video from another reported attack in Telmens on April 21st
I believe the function of this assembly is to hold the cylinder away from the base of the bomb, so during impact the cylinder doesn't end up buried in the ground, preventing the release of gas. There's also a slot in the casing of the barrel bomb, next to the end of the cylinder, which could be there to allow gas to be released on impact. This would strongly suggest more effort has gone into the design of these munitions than simply placing a gas cylinder inside a barrel bomb.
More videos showing the remains of chemical barrel bombs can be found here, and the remaining Daniele Raineri photographs can be found here.